Yabasic


Table of Contents

1. Introduction
About this document
About yabasic
2. The yabasic-program under Windows
Starting yabasic
Options
The context Menu
3. The yabasic-program under Unix
Starting yabasic
Options
Setting defaults
4. Command line options of yabasic
5. All commands and functions of yabasic listed by topic
Numbers with base 2 or 16
Number processing and conversion
Conditions and control structures
Data keeping and processing
String processing
File operations and printing
Subroutines and libraries
Invoking functionality outside of yabasic
Other commands
Graphics and printing
The foreign function interface
6. Some features and general concepts of yabasic
Logical shortcuts
Conditions and expressions
References on arrays
Specifying Filenames under Windows
Escape-sequences
Creating a standalone program from your yabasic-program
Interaction with functions from a non-yabasic library or dll
7. All commands and functions of yabasic grouped alphabetically
A
B
C
D
E
F
G
H
I
L
M
N
O
P
R
S
T
U
V
W
X
Special characters
8. A few example programs
A very simple program
Graphics with bitmaps
A menu to choose from
9. The Copyright of yabasic

Chapter 1. Introduction

About this document

This document describes yabasic. You will find information about the yabasic interpreter (the program yabasic under Unix or yabasic.exe under Windows) as well as the language (which is, of course, a sort of basic) itself.

This document applies to version 2.86 of yabasic

However, this document does not contain the latest news about yabasic or a FAQ. As such information tends to change rapidly, it is presented online only at www.yabasic.de.

Although basic has its reputation as a language for beginning programmers, this is not an introduction to programming at large. Rather this text assumes, that the reader has some (moderate) experience with writing and starting computer programs.

About yabasic

yabasic is a traditional basic interpreter. It understands most of the typical basic-constructs, like goto, gosub, line numbers, read, data or string-variables with a trailing '$'. But on the other hand, yabasic implements some more advanced programming-constructs like subroutines or libraries (but not objects). yabasic works much the same under Unix and Windows.

yabasic puts emphasis on giving results quickly and easily; therefore simple commands are provided to open a graphic window, print the graphics or control the console screen and get keyboard or mouse information. The example below opens a window, draws a circle and prints the graphic:

open window 100,100
open printer
circle 50,50,40
text 10,50,"Press any key to get a printout"
clear screen
inkey$
close printer
close window

This example has fewer lines, than it would have in many other programming languages. In the end however yabasic lacks behind more advanced and modern programming languages like C++ or Java. But as far as it goes it tends to give you results more quickly and easily.

Chapter 2. The yabasic-program under Windows

Starting yabasic

Once, yabasic has been set up correctly, there are three ways to start it:

  1. Right click on your desktop: The desktop menu appears with a submenu named new. From this submenu choose yabasic. This will create a new icon on your desktop. If you right click on this icon, its context menu will appear; choose Execute to execute the program.

  2. As a variant of the way described above, you may simply create a file with the ending .yab (e.g. with your favorite editor). Everything else then works as described above.

  3. From the start-menu: Choose yabasic from your start-menu. A console-window will open and you will be asked to type in your program. Once you are finished, you need to type return twice, and yabasic will parse and execute your program.

    Note

    This is not the preferred way of starting yabasic ! Simply because the program, that you have typed, can not be saved and will be lost inevitably ! There is no such thing as a save-command and therefore no way to conserve the program, that you have typed. This mode is only intended for quick hacks, and short programs.

Options

Under Windows yabasic will mostly be invoked by double-clicking on an appropriate icon; this way you do not have a chance to specify any of the command line options below. However, advanced users may change the librarypath in the registry, which has the same effect as specifying it as an option on the command line.

See the chapter on options for a complete list of all options, either on Unix or Windows.

The context Menu

Like every other icon under Windows, the icon of every yabasic-program has a context menu offering the most frequent operations, that may be applied to a yabasic-program.

Execute

This will invoke yabasic to execute your program. The same happens, if you double click on the icon.

Edit

notepad will be invoked, allowing you to edit your program.

View docu

This will present the embedded documentation of your program. Embedded documentation is created with the special comment doc.

Chapter 3. The yabasic-program under Unix

Starting yabasic

If your system administrator (vulgo root) has installed yabasic correctly, there are three ways to start it:

  1. You may use your favorite editor (emacs, vi ?) to put your program into a file (e.g. foo). Make sure that the very first line starts with the characters '#!' followed by the full pathname of yabasic (e.g. '#!/usr/local/bin/yabasic'). This she-bang-line ensures, that your Unix will invoke yabasic to execute your program (see also the entry for the hash-character). Moreover, you will need to change the permissions of your yabasic-program foo, e.g. chmod u+x foo. After that you may invoke yabasic to invoke your program by simply typing foo (without even mentioning yabasic). However, if your PATH-variable does not contain a single dot ('.') you will have to type the full pathname of your program: e.g. /home/ihm/foo (or at least ./foo).

  2. Save your program into a file (e.g. foo) and type yabasic foo. This assumes, that the directory, where yabasic resides, is contained within your PATH-variable.

  3. Finally your may simply type yabasic (maybe it will be necessary to include its full pathname). This will make yabasic come up and you will be asked to type in your program. Once you are finished, you need to type return twice, and yabasic will parse and execute your program.

    Note

    This is not the preferred way of starting yabasic ! Simply because the program, that you have typed, can not be saved and will be lost inevitably ! There is no such thing as a save-command and therefore no way to conserve the program, that you have typed. This mode is only intended for quick hacks, and short programs, i.e. for using yabasic as some sort of fancy desktop calculator.

Options

yabasic accepts a number of options on the command line.

See chapter on options for a complete list of all options, either on Unix or Windows.

Setting defaults

If you want to set some options once for all, you may put them into your X-Windows resource file. This is usually the file .Xresources or some such within your home directory (type man X for details).

Here is a sample section, which may appear within this file:

yabasic*foreground: blue
yabasic*background: gold
yabasic*geometry: +10+10
yabasic*font: 9x15

This will set the foreground color of the graphic-window to blue and the background color to gold. The window will appear at position 10,10 and the text font will be 9x15.

Chapter 4. Command line options of yabasic

Here are the options, that yabasic accepts on the command line (both under Unix and Windows).

All the options below may be abbreviated (and one hyphen may be dropped), as long as the abbreviation does not become ambiguous. For example, you may write -e instead of --execute.

--help or -?

Prints a short help message, which itself describes two further help-options.

--version

Prints the version of yabasic.

--infolevel INFOLEVEL

Change the infolevel of yabasic, where INFOLEVEL can be one of debug, note, warning, error, fatal and bison (the default is warning). This option changes the amount of debugging-information yabasic produces. However, normally only the author of yabasic (me !) would want to change this.

--execute A-PROGRAM-AS-A-SINGLE-STRING

With this option you may specify some yabasic-code to be executed right away. This is useful for very short programs, which you do not want to save to a file. If this option is given, yabasic will not read any code from a file. E.g.

yabasic -e 'for a=1 to 10:print a*a:next a'

prints the square numbers from 1 to 10.

--bind NAME-OF-STANDALONE-PROGRAM

Create a standalone program (whose name is specified by NAME-OF-STANDALONE-PROGRAM) from the yabasic-program, that is specified on the command line. See the section about creating a standalone-program for details.

--geometry +X-POSITION+Y-POSITION

Sets the position of the graphic window, that is opened by open window (the size of this window, of course, is specified within the open window-command). An example would be -geometry +20+10, which would place the graphic window 10 pixels below the upper border and 20 pixels right of the left border of the screen. This value cannot be changed, once yabasic has been started.

-fg FOREGROUND-COLOR or --foreground FOREGROUND-COLOR

Unix only. Define the foreground color for the graphics-window (that will be opened with open window). The usual X11 color names, like red, green, … are accepted. This value cannot be changed, once yabasic has been started.

-bg BACKGROUND-COLOR or --background BACKGROUND-COLOR

Unix only. Define the background color for the graphics-window. The usual X11 color names are accepted. This value cannot be changed, once yabasic has been started.

--display X11-DISPLAY-SPECIFICATION

Unix only. Specify the display, where the graphics window of yabasic should appear. Normally this value will be already present within the environment variable DISPLAY.

--font NAME-OF-FONT

Under Unix. Name of the font, which will be used for text within the graphics window.

--font NAME-OF-FONT

Under Windows. Name of the font, which will be used for graphic-text; can be any of decorative, dontcare, modern, roman, script, swiss. You may append a fontsize (measured in pixels) to any of those fontnames; for example -font swiss30 chooses a swiss-type font with a size of 30 pixels.

--docu NAME-OF-A-PROGRAM

Print the embedded documentation of the named program. The embedded documentation of a program consists of all the comments within the program, which start with the special keyword doc. This documentation can also be seen by choosing the corresponding entry from the context-menu of any yabasic-program.

--check

Check for possible compatibility problems within your yabasic-program. E.g. this option reports, if you are using a function, that has recently changed.

--librarypath DIRECTORY-WITH-LIBRARIES

Change the directory, wherein libraries will be searched and imported (with the import-command). See also import for more information about the way, libraries are searched.

--

Do not try to parse any further options; rather pass the subsequent words from the commandline to yabasic.

Chapter 5. All commands and functions of yabasic listed by topic

Numbers with base 2 or 16

In addition to the usual decimal notation (e.g. 1234), yabasic also supports numeric literals with base 2 or 16; examples are 0b10011 (the number 19, written with base 2) or 0x34AF (the number 13487, written with base 16) respectively. Please note that these numbers (apart from the way you write them into your program) are no different from ordinary numbers and can be used in any place, where a normal number with base 10 would fit. E.g. you may compute the sine sin(0b110); so the base 2 (or 16) is just a different way of representation.

See bin$, hex$ or dec for related functions.

Number processing and conversion

abs()
returns the absolute value of its numeric argument
acos()
returns the arcus cosine of its numeric argument
and()
the bitwise arithmetic and
asin()
returns the arcus sine of its numeric argument
atan()
returns the arctangent of its numeric argument
bin$()
converts a number into a sequence of binary digits
cos()
return the cosine of its single argument
dec()
convert a base 2 or base 16 number into decimal form
eor()
compute the bitwise exclusive or of its two arguments
euler
another name for the constant 2.71828182864
exp()
compute the exponential function of its single argument
frac()
return the fractional part of its numeric argument
int()
return the integer part of its single numeric argument
ceil()
compute the ceiling for its (float) argument
floor()
compute the floor for its (float) argument
round()
round its argument to the nearest integer
log()
compute the natural logarithm
max()
return the larger of its two arguments
min()
return the smaller of its two arguments
mod
compute the remainder of a division
bitnot()
the bitwise arithmetic not
or()
arithmetic or, used for bit-operations
pi
a constant with the value 3.14159
ran()
return a random number
shl()
shift its argument bitwise to the left
shr()
shift its argument bitwise to the right
sig()
return the sign of its argument
sin()
return the sine of its single argument
sqr()
compute the square of its argument
sqrt()
compute the square root of its argument
tan()
return the tangent of its argument
xor()
compute the exclusive or
** or ^
raise its first argument to the power of its second

Conditions and control structures

and
logical and, used in conditions
break
breaks out of one or more loops or switch statements
case
mark the different cases within a switch-statement
continue
start the next iteration of a for-, do-, repeat- or while-loop
default
mark the default-branch within a switch-statement
do
start a (conditionless) do-loop
else
mark an alternative within an if-statement
elsif
starts an alternate condition within an if-statement
end
terminate your program
endif
ends an if-statement
false
a constant with the value of 0
fi
another name for endif
for
starts a for-loop
gosub
continue execution at another point within your program (and return later)
goto
continue execution at another point within your program (and never come back)
if
evaluate a condition and execute statements or not, depending on the result
label
mark a specific location within your program for goto, gosub or restore
loop
marks the end of an infinite loop
next
mark the end of a for loop
not
negate a logical expression; can be written as !
on gosub
jump to one of multiple gosub-targets
on goto
jump to one of many goto-targets
on interrupt
change reaction on keyboard interrupts
logical or
logical or, used in conditions
bitwise or
arithmetic or, used for bit-operations
pause
pause, sleep, wait for the specified number of seconds
repeat
start a repeat-loop
return
return from a subroutine or a gosub
sleep
pause, sleep, wait for the specified number of seconds
switch
select one of many alternatives depending on a value
then
tell the long from the short form of the if-statement
true
a constant with the value of 1
until
end a repeat-loop
wait
pause, sleep, wait for the specified number of seconds
wend
end a while-loop
while
start a while-loop
:
separate commands from each other

Data keeping and processing

arraydim()
returns the dimension of the array, which is passed as an array reference
arraysize()
returns the size of a dimension of an array
data
introduces a list of data-items
dim
create an array prior to its first use
read
read data from data-statements
redim
create an array prior to its first use. A synonym for dim
restore
reposition the data-pointer

String processing

asc()
accepts a string and returns the position of its first character within the ascii charset
chomp$()
remove a single trailing newline from its string-argument; if the string does not end in a newline, the string is returned unchanged
chr$()
accepts a number and returns the character at this position within the ascii charset
glob()
check if a string matches a simple pattern
hex$()
convert a number into hexadecimal
instr()
searches its second argument within the first; returns its position if found
rinstr()
find the rightmost occurrence of one string within the other
left$()
return (or change) left end of a string
len()
return the length of a string
lower$()
convert a string to lower case
ltrim$()
trim spaces at the left end of a string
mid$()
return (or change) characters from within a string
right$()
return (or change) the right end of a string
split()
split a string into many strings
str$()
convert a number into a string
token()
split a string into multiple strings
trim$()
remove leading and trailing spaces from its argument
rtrim$()
trim spaces at the right end of a string
upper$()
convert a string to upper case
val()
converts a string to a number

File operations and printing

at()
can be used in the print-command to place the output at a specified position
beep
ring the bell within your computer; a synonym for bell
bell
ring the bell within your computer (just as beep)
clear screen
erases the text window
close
close a file, which has been opened before
close printer
stops printing of graphics
print color
print with color
print colour
see print color
eof
check, if an open file contains data
getscreen$()
returns a string representing a rectangular section of the text terminal
inkey$
wait, until a key is pressed
input
read input from the user (or from a file) and assign it to a variable
line input
read in a whole line of text and assign it to a variable
open
open a file
open printer
open printer for printing graphics
print
Write to terminal or file
putscreen
draw a rectangle of characters into the text terminal
reverse
print reverse (background and foreground colors exchanged)
screen
as clear screen clears the text window
seek()
change the position within an open file
tell
get the current position within an open file
using
Specify the format for printing a number
#
either a comment or a marker for a file-number
at
can be used in the print-command to place the output at a specified position
@
synonymous to at
;
suppress the implicit newline after a print-statement

Subroutines and libraries

end sub
ends a subroutine definition
export
mark a function as globally visible
import
import a library
local
mark a variable as local to a subroutine
numparams
return the number of parameters, that have been passed to a subroutine
return
return from a subroutine or a gosub
static
preserves the value of a variable between calls to a subroutine
step
specifies the increment step in a for-loop
sub
declare a user defined subroutine

Invoking functionality outside of yabasic

system()
hand the name of an external command over to your operating system and return its exitcode
system$()
hand the name of an external command over to your operating system and return its output

Other commands

bind()
binds a yabasic-program and the yabasic-interpreter together into a standalone program
compile
compile a string with yabasic-code on the fly
date$
returns a string with various components of the current date
doc
special comment, which might be retrieved by the program itself
docu$
special array, containing the contents of all docu-statement within the program
error
raise an error and terminate your program
execute$()
execute a user defined subroutine, which must return a string
execute()
execute a user defined subroutine, which must return a number
exit
terminate your program
pause
pause, sleep, wait for the specified number of seconds
peek
retrieve various internal information
peek$
retrieve various internal string-information
poke
change selected internals of yabasic
rem
start a comment
sleep
pause, sleep, wait for the specified number of seconds
time$
return a string containing the current time
to
this keyword appears as part of other statements
wait
pause, sleep, wait for the specified number of seconds
//
starts a comment
:
separate commands from each other

Graphics and printing

backcolor
change color for background of graphic window
box
draw a rectangle. A synonym for rectangle
circle
draws a circle in the graphic-window
clear
erase circles, rectangles or triangles
clear window
clear the graphic window and begin a new page, if printing is under way
close curve
close a curve, that has been drawn by the line-command
close window
close the graphics-window
color
change color for any subsequent drawing-command
dot
draw a dot in the graphic-window
fill
draw a filled circles, rectangles or triangles
getbit$()
return a string representing the bit pattern of a rectangle within the graphic window
line
draw a line
mouseb
extract the state of the mousebuttons from a string returned by inkey$
mousemod
return the state of the modifier keys during a mouseclick
mousex
return the x-position of a mouseclick
mousey
return the y-position of a mouseclick
new curve
start a new curve, that will be drawn with the line-command
open window
open a graphic window
putbit
draw a rectangle of pixels encoded within a string into the graphics window
rectangle
draw a rectangle
triangle
draw a triangle
text
write text into your graphic-window
window origin
move the origin of a window

The foreign function interface

foreign_buffer_alloc$()
Create a new buffer for use in a foreign function call
foreign_buffer_dump$()
return the content of a buffer as a hex-encoded string
foreign_buffer_free()
free a foreign buffer
foreign_buffer_get()
extract a number from a foreign buffer
foreign_buffer_get$()
extract a string from a foreign buffer
foreign_buffer_get_buffer$()
take a buffer and construct a handle to a second buffer from its content
foreign_buffer_set
store a given value within a buffer
foreign_buffer_set_buffer
store a pointer to one buffer within another buffer
foreign_buffer_size()
return the size of the foreign buffer
foreign_function_call()
call a function (returning a number) from a non-yabasic library or dll
foreign_function_call$()
call a function (returning a string or a buffer) from a non-yabasic library or dll
foreign_function_size()
Abbreviations for foreign_buffer_ and foreign_function_
frnbf_ and frnfn_
return the size of one of the types available for foreign function calls

Chapter 6. Some features and general concepts of yabasic

This chapter presents some general concepts and terms, which deserve a description on their own, but are not associated with a single command or function in yabasic. Most of these topics do not lend themselves to be read alone, rather they might be read (or skimmed) as background material if an entry from the alphabetical list of commands refers to them.

Logical shortcuts

Logical shortcuts are no special language construct and there is no keyword for them; they are just a way to evaluate logical expressions. Logical expressions (i.e. a series of conditions or comparisons joined by and or or) are only evaluated until the final result of the expression can be determined. An example:

if (a<>0 and b/a>2) print "b is at least twice as big as a"

The logical expression a<>0 and b/a>2 consists of two comparisons, both of which must be true, if the print statement should be executed. Now, if the first comparison (a<>0) is false, the whole logical expression can never be true and the second comparison (b/a>2) need not be evaluated.

This is exactly, how yabasic behaves: The evaluation of a composed logical expressions is terminated immediately, as soon as the final result can be deduced from the already evaluated parts.

In practice, this has the following consequences:

  • If two or more comparisons are joined with and and one comparison results in false, the logical expression is evaluated no further and the overall result is false.

  • If two or more comparisons are joined with or and one comparison results in true, the logical expression is evaluated no further and the result is true.

Nice, but whats this good for ?, I hear you say. Well, just have another look at the example, especially the second comparison (b/a>2); dividing b by a is potentially hazardous: If a equals zero, the expression will cause an error and your program will terminate. To avoid this, the first part of the comparison (a<>0) checks, if the second one can be evaluated without risk. This pre-checking is the most common usage and primary motivation for logical shortcuts (and the reason why most programming languages implement them).

Conditions and expressions

Well, bottomline there is no difference or distinction between conditions and expressions, at least as yabasic is concerned. So you may assign the result of comparisons to variables or use an arithmetic expression or a simple variable within a condition (e.g. within an if-statement). So the constructs shown in the example below are all totally valid:

input "Please enter a number between 1 and 10: " a

rem   Assigning the result of a comparison to a variable
okay=a>=1 and a<=10

rem   Use a variable within an if-statement
if (not okay) error "Wrong, wrong !"

So conditions and expressions are really the same thing (at least as long as yabasic is concerned). Therefore the terms conditions and expression can really be used interchangeably, at least in theory. In reality the term condition is used in connection with if or while whereas the term expression tends to be used more often within arithmetic context.

References on arrays

References on arrays are the only way to refer to an array as a whole and to pass it to subroutines or functions like arraydim or arraysize. Whereas (for example) a(2) designates the second element of the array a, a() (with empty braces) refers to the array a itself. a() is called an array reference.

If you pass an array reference to one of your own subroutines, you need to be aware, that the subroutine will be able to modify the array you have passed in. So passing an array reference does not create a copy of the array; this has some interesting consequences:

  • Speed and space: Creating a copy of an array would be a time (and resource) consuming operation; passing just a reference is cheap and fast.

  • Returning many values: A subroutine, that wants to give back more than one value, may require an array reference among its arguments and then store its many return values within this array. This is the only way to return more than one value from a subroutine.

Specifying Filenames under Windows

As you probably know, windows uses the character '\' to separate the directories within a pathname; an example would be C:\yabasic\yabasic.exe (the usual location of the yabasic executable). However, the very same character '\' is used to construct escape sequences, not only in yabasic but in most other programming languages.

Therefore the string "C:\t.dat" does not specify the file t.dat within the directory C:; this is because the sequence '\t' is translated into the tab-character. To specify this filename, you need to use the string "C:\\t.dat" (note the double slash '\\').

Escape-sequences

Escape-sequences are the preferred way of specifying 'special' characters. They are introduced by the '\'-character and followed by one of a few regular letters, e.g. '\n' or '\r' (see the table below).

Escape-sequences may occur within any string at any position; they are replaced at parsetime (opposed to runtime), i.e. as soon as yabasic discovers the string, with their corresponding special character. As a consequence of this len("\a") returns 1, because yabasic replaces "\a" with the matching special character just before the program executes.

Table 6.1. Escape sequences

Escape SequenceMatching special character
\nnewline
\ttabulator
\vvertical tabulator
\bbackspace
\rcarriage return
\fformfeed
\aalert (i.e. a beeping sound)
\\backslash
\'single quote
\"double quote
\xHEXchr$(HEX) (see below)

Note, that an escape sequences of the form \xHEX allows one to encode arbitrary characters as long as you know their position (as a hex-number) within the ascii-charset: For example \x012 is transformed into the character chr$(18) (or chr$(dec("12",16)). Note that \x requires a hexa-decimal number (and the hexadecimal string "12" corresponds to the decimal number 18).

Creating a standalone program from your yabasic-program

Sometimes you may want to give one of your yabasic-programs to other people. However, what if those other people do not have yabasic installed ? In that case you may create a standalone-program from your yabasic-program, i.e. an executable, that may be executed on its own, standalone, even (and especially !) on computers, that do not have yabasic installed. Having created a standalone program, you may pass it around like any other program (e.g. one written in C) and you can be sure that your program will execute right away.

Such a standalone-program is simply created by copying the full yabasic-interpreter and your yabasic-program (plus all the libraries it does import) together into a single, new program, whose name might be chosen at will (under windows of course it should have the ending .exe). If you decide to create a standalone-program, there are three bits in yabasic, that you may use:

  • The bind-command, which does the actual job of creating the standalone program from the yabasic-interpreter and your program.

  • The command-line Option --bind (see options), which does the same from the command-line.

  • The special peek("isbound"), which may be used to check, if the yabasic-program containing this peek is bound to the interpreter as part of a standalone program.

With these bits you know enough to create a standalone-program. Actually there are two ways to do this: on the command line and from within your program.

Creating a standalone-program from the command line

Let's say you have the following very simple program within the file foo.yab:

print "Hello World !"

Normally you would start this yabasic-program by typing yabasic foo.yab and as a result the string Hello World ! would appear on your screen. However, to create a standalone-program from foo.yab you would type:

yabasic -bind foo.exe foo.yab

This command does not execute your program foo.yab but rather create a standalone-program foo.exe. Note: under Unix you would probably name the standalone program foo or such, omitting the windows-specific ending .exe.

Yabasic will confirm by printing something like: ---Info: Successfully bound 'yabasic' and 'foo.yab' into 'foo.exe'.

After that you will find a program foo.exe (which must be made executable with the chmod-command under Unix first). Now, executing this program foo.exe (or foo under Unix) will produce the output Hello World !.

This newly created program foo.exe might be passed around to anyone, even if he does not have yabasic installed.

Creating a standalone-program from within your program

It is possible to write a yabasic-program, that binds itself to the yabasic-interpreter. Here is an example:

if (!peek("isbound")) then
  bind "foo"
  print "Successfully created the standalone executable 'foo' !"
  exit
endif

print "Hello World !"

If you run this program (which may be saved in the file foo.yab) via yabasic foo.yab, the peek("isbound") in the first line will check, if the program is already part of a standalone-program. If not (i.e. if the yabasic-interpreter and the yabasic-program are separate files) the bind-command will create a standalone program foo containing both. As a result you would see the output Successfully created the standalone executable 'foo' !. Note: Under Windows you would probably choose the filename foo.exe.

Now, if you run this standalone executable foo (or foo.exe), the very same yabasic-program that is shown above will be executed again. However, this time the peek("isbound") will return TRUE and therefore the condition of the if-statement is false and the three lines after then are not executed. Rather the last print-statement will run, and you will see the output Hello World !.

That way a yabasic-program may turn itself into a standalone-program.

Points to consider before creating a standalone program

  • The new standalone program will be at least as big as the interpreter itself, which is typically a few hundred kilobytes.

  • There is no easy way to extract your yabasic-program from within the standalone program: If you ever want to change it, you should keep it around as a separate file.

  • If a new version of yabasic becomes available, you might want to recreate your standalone program to take advantage of bugfixes and improvements.

See also

The bind-command, the peek-function and the command line options.

Interaction with functions from a non-yabasic library or dll

Note

Under Unix, depending on the way yabasic has been built, this feature might have been disabled; the error message in this case will read like this build of yabasic does not support calling foreign libraries. To resolve this issue, you are invited to contact the maintainer.

Note

This is interesting, but somewhat advanced stuff. You will need a good understanding of various concepts of the C-language, especially pointers and structures as well as allocating and freeing blocks of memory. Please be aware, that mistakes or errors during calls to foreign functions or buffers may easily crash yabasic.

Yabasic allows to employ functionality from an external library; i.e. from a library, which is not written in yabasic, but rather in C; such a library is called a foreign library, as opposed to a library written in yabasic itself. Calling out to a foreign library can be useful, if such a library provides functionality, that can not be replicated in yabasic itself and for which a commandline-interface (which could be used via system) does not exist or is too cumbersome or slow. Examples would be libraries libVLC or libcurl which offer the functionality of vlc or curl to other programs, especially programs written in yabasic.

The foreign function interface of yabasic relies on the great libffi-library, a library making it easy to call other libraries dynamicaaly and the established standard for this task.

Some Background

Libraries

Libraries (e.g. libcurl) are meant to provide functionality to other programs (here: yabasic and your yabasic-program). Libraries and programs must be linked together; this can happen either statically at compile-time or dynamically during the excution of the program. For yabasic as the program, static linking happens at the time, yabasic itself is build, whereas dynamic linking happen during the execution and under control of your yabasic-program. So the foreign function interface deals with dynamic (or runtime) linking to external libraries. This linking is done by yabasic behind the scene, when you invoke foreign_function_call; this function, after loading the library, directly calls the specified function therein.

Which functions are available differs from library to library and you should already have this information before you try the library with yabasic.

Types

If you want to use a function from a foreign library, you will need to deal with the fact, that each function requires several parameters and returns exactly one. These parameters have a wide variety of types which need to be mapped to the two types (numbers and strings) known by yabasic. Here are the types available for foreign functions, grouped by the way, they are handled in yabasic:

uint8,int8,uint16,int16,uint32,int32,uint64,int64,float,double,char,short,int,long

In C all these types are used to represent numbers (integer or floating point) with various degrees of precision. When invoking foreign_function_call you need to pass strings, which specify the right type as well as the actual yabasic-value, which will then be converted accordingly. Which types a foreign function expects can be looked up e.g. from its manpage.

string

Strings for foreign functions directly map to strings of yabasic. So if you specify this type for a parameter of a foreign function, the matching value is simply a yabasic string. If you specify string as the return value of a foreign function you should use the variant of calling it, which returns a string, i.e. foreign_function_call$.

buffer

You should specify a buffer as the type of a parameter or the return type, if the foreign function expects a structure or a pointer to a memory area; see structures and buffers for details.

Three simple examples

Computing the cosine

This first example prints the cosine of 2, not by using yabasics own cos-function but by calling out to the standard C-library:

if peek$("os")="windows" then
  lib$ = "msvcrt.dll"
else
  lib$ = "libm.so.6"
endif

print "cos(2): ",foreign_function_call(lib$,"double","cos","double",2)

The first lines determine the name of the library, which is different under Unix and Windows. The call to foreign_function_call than just states the name of the library, the return type ("double") of the function and then its name ("cos"), as well as type and value (2) of its argument. The final result -0.416147 then is the same as from the the internal cos-function, which is no surprise, because yabasic is already statically linked to the standard C-library and uses its function to compute the cosine.

Searching a string within another string

A second example:

if peek$("os")="windows" then
  lib$ = "msvcrt.dll"
else
  lib$ = "libm.so.6"
endif

print foreign_function_call$(lib$,"string","strstr","string","foobar","string","ob","options","copy_string_result")

This example calls the strstr-function from the standard C-library; this function accepts two string arguments and returns a string, which is the first (if any) appearance of the second string within the first one (remark: this function makes more sense in C than in yabasic). Please note the option "copy_string_result", which advices yabasic to return a copy of the result of strstr; otherwise your program might crash, because strstr simply returns a pointer to a part of its first argument, a string that will later be freed by yabasic.

Showing a message box under Windows

This example is windows only; it shows a standard Windows message box with the given title and message:

message_box("Hello World !","Message from yabasic")

sub message_box(message$, title$)
  msgptr$ = foreign_buffer_alloc$(len(message$)+1)
  foreign_buffer_set msgptr$, 0, message$
  titleptr$ = foreign_buffer_alloc$(len(title$)+1)
  foreign_buffer_set titleptr$, 0, title$
  hwnd$ = foreign_function_call$("user32.dll", "buffer", "GetActiveWindow")
  ret = foreign_function_call("user32.dll", "int32", "MessageBoxA", "buffer", hwnd$, "buffer", msgptr$, "buffer", titleptr$, "uint32", 0)
  foreign_buffer_free msgptr$
  foreign_buffer_free titleptr$
  return ret
end sub

The relevant Windows-function MessageBoxA is found within the library user32.dll; most of the example deals with properly allocating, handling and freeing buffers to hold the supplied text-snippets. Thanx to Jean-Marc Duro for this example.

Internal steps during a call to a foreign function

A remark on libffi: this is the library which allows yabasic to call functions from other libraries libffi is used by many other programming-languages for the same purpose; in yabasic it is linked statically (rather than dynamically) so that its functionality is available right from the start. Summing up: libffi itself need not be loaded but helps to call functions from other loaded libraries.

Here is the sequence of events during a foreign function call (e.g. foreign_function_call):

  • Yabasic parses the type specifications and argument values provided and collects the necessary information for libffi.

  • The named library is loaded with the appropriate call (which is different under Windows and Unix). This step might easily fail, e.g. if you misspelled the name of the library or your system cannot find the library.

  • With the help of libffi the named function is invoked.

  • If you specified the option unload_library, the library that has been loaded is unloaded again.

  • The return value of the function is converted to a form suitable for yabasic and your program continues.

Errors are reported during every step.

Abbreviations for long names

Yabasics functions for dealing with foreign libraries start with foreign_function or foreign_buffer (e.g. foreign_buffer_alloc). To help in typing, these names can all be abbreviated by contracting foreign_function into frnfn and foreign_buffer into frnbf. In the examples below, both forms appear.

Structurs and buffers

The C-language provides a wide variety of simple datatypes (like numbers an strings) and allows to aggregate simple datatypes to structures such a structure contains a set of simple types arranged without overlap (but sometimes with gaps). Yabasic on itself does not know the internals of a structure but rather treats it as a uniform buffer. Structure and buffer are just flipsides of the same memory area viewed either from C or yabasic. For your yabasic-program a buffer is represented by a handle, which is just a simple printable string (containing the size and the memory adress).

The detailed knowledge about the simple types within a structure must be coded into your program, which uses the command (or function) foreign_buffer_set and foreign_buffer_get. Both functions require type and offset (which needs to be looked up in documentation of the foreign library) of the simple type within the structure and a handle to the buffer, which contains the structure.

Beeing essentially a memory area, a buffer is created with foreign_buffer_alloc and destroyed with foreign_buffer_free if needed no more.

Besides representing a structure, a buffer can also provide room to store raw areas of memory for use by the foreign library; example might be image- or sound-content.

Two more complex examples

Dealing with time

The example below deals with the time functions from the standard C-library; some of them deal with the tm structure for keeping the segmented time; to understand the example to follow it is helpful to have the tm-structure at hand; see below. In addition it might be helpful to consult the manpages of the various C-functions (e.g. localtime)involved.

struct tm {
    int tm_sec;    /* Seconds (0-60) */
    int tm_min;    /* Minutes (0-59) */
    int tm_hour;   /* Hours (0-23) */
    int tm_mday;   /* Day of the month (1-31) */
    int tm_mon;    /* Month (0-11) */
    int tm_year;   /* Year - 1900 */
    int tm_wday;   /* Day of the week (0-6, Sunday = 0) */
    int tm_yday;   /* Day in the year (0-365, 1 Jan = 0) */
    int tm_isdst;  /* Daylight saving time */
};
    

The example plays with the two forms of keeping the time, either as unix-time (number of seconds since epoch) or as a segmented time (sec, min, etc.). The six steps are each introduced by comments, please see below.

# First: Determine the correct library depending on OS
#
if peek$("os")="windows" then
  lib$ = "msvcrt.dll"
else
  lib$ = "libm.so.6"
endif

# Second: Get the unix-time
#
# time() has a pointer argument to store the result (in addition to returning it)
# we pass NULL, so only the return value is relevant
#
null$ = foreign_buffer_alloc$(-1)
now = foreign_function_call(lib$,"int","time","buffer",null$)
print "Seconds since the epoch: ",now

# Third: Convert the unix-time to a segmented time
#
# localtime() does not accept the time-value as an argument, but rather requires a pointer
# to the time-value, so we construct a buffer for one int and put in our value
now$ = foreign_buffer_alloc$(foreign_function_size("int"))
foreign_buffer_set now$,0,"int",now
# Dump the buffer for educational purpose
print "Dump of buffer:          ",foreign_buffer_dump$(now$)
# localtime() returns a structure with the componentes (year, day, sec, etc.) as elements
local$ = foreign_function_call$(lib$,"buffer","localtime","buffer",now$)

# Fourth: Get the current year from the resulting buffer
#
# assuming, that year is the sixth element of the structure
# so offset is 5
offset = 5 * foreign_function_size("int")
year = foreign_buffer_get(local$,offset,"int")
print "Current year:            ", year + 1900


# Fifth: manipulate the segmented time
#
# set year to something else
foreign_buffer_set local$,offset,"int",year-50


# Sixth: convert time-structure from localtime into ascii
#
print "50 years back:           ", foreign_function_call$(lib$,"string","asctime","buffer",local$)

On my computer this program produces the following output:

Seconds since the epoch: 1559014899
Dump of buffer:          F3ADEC5C
Current year:            2019
50 years back:           Tue May 28 05:41:39 1969  

Getting the version of libcurl

This final example just invokes libcurl to report its version. This is somewhat involved, because the matching function curl_version_info (see its man-page) returns a structure, which contains a pointer to a string, as can be seen from the structures definition:

typedef struct {
  CURLversion age;          /* see description below */
  const char *version;      /* human readable string */
  unsigned int version_num; /* numeric representation */
  const char *host;         /* human readable string */
  int features;             /* bitmask, see below */
  char *ssl_version;        /* human readable string */
  long ssl_version_num;     /* not used, always zero */
  const char *libz_version; /* human readable string */
  const char * const *protocols; /* protocols */

  ...                       /* more lines omitted */
  
} curl_version_info_data;
    

Please note, that the yabasic-code below uses abbreviations (e.g. frnfn_call instead of foreign_function_call.

# Get structure with version info
info$ = frnfn_call$("libcurl.so.4","buffer","curl_version_info","int",1)
# dump it for reference
print frnbf_dump$(info$,32)
# assume, that the pointer to version string is at offset 8
sinfo$ = frnbf_get_buffer$(info$,8)
# print readable version
print frnbf_get$(sinfo$,0,10)

The printing of frnbf_dump gives a hint on the internal offsets within the structure and helps to determine that offset of 8 for the next call.

On my system this program produces 7.61.1 for the version of curl.

Chapter 7. All commands and functions of yabasic grouped alphabetically

A

abs() — returns the absolute value of its numeric argument
acos() — returns the arcus cosine of its numeric argument
and — logical and, used in conditions
and() — the bitwise arithmetic and
arraydim() — returns the dimension of the array, which is passed as an array reference
arraysize() — returns the size of a dimension of an array
asc() — accepts a string and returns the position of its first character within the ascii charset
asin() — returns the arcus sine of its numeric argument
at() — can be used in the print-command to place the output at a specified position
atan() — returns the arctangent of its numeric argument

Name

abs() — returns the absolute value of its numeric argument

Synopsis

y=abs(x)

Description

If the argument of the abs-function is positive (e.g. 2) it is returned unchanged, if the argument is negative (e.g. -1) it is returned as a positive value (e.g. 1).

Example

print abs(-2),abs(2)
          

This example will print 2 2

See also

sig


Name

acos() — returns the arcus cosine of its numeric argument

Synopsis

x=acos(angle)

Description

acos is the arcus cosine-function, i.e. the inverse of the cos-function. Or, more elaborate: It Returns the angle (in radians, not degrees !), which, fed to the cosine-function will produce the argument passed to the acos-function.

Example

print acos(0.5),acos(cos(pi))
          

This example will print 1.0472 3.14159 which are π/3 and π respectively.

See also

cos, asin


Name

and — logical and, used in conditions

Synopsis

if a and b …
while a and b …

Description

Used in conditions (e.g within if, while or until) to join two expressions. Returns true, if and only if its left and right argument are both true and false otherwise.

Note, that logical shortcuts may take place.

Example

input "Please enter a number" a
if (a>=1 and a<=9) print "your input is between 1 and 9"
          

See also

or,not


Name

and() — the bitwise arithmetic and

Synopsis

x=and(a,b)

Description

Used to compute the bitwise and of both its argument. Both arguments are treated as binary numbers (i.e. a sequence of digits 0 and 1); a bit of the resulting value will then be 1, if both arguments have a 1 at this position in their binary representation.

Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to and.

Example

print and(6,3)
          

This will print 2. This result is clear, if you note, that the binary representation of 6 and 3 are 110 and 011 respectively; this will yield 010 in binary representation or 2 as decimal.

See also

or, eor and bitnot


Name

arraydim() — returns the dimension of the array, which is passed as an array reference

Synopsis

a=arraydim(b())

Description

If you apply the arraydim()-function on a one-dimensional array (i.e. a vector) it will return 1, on a two-dimensional array (i.e. a matrix) it will return 2, and so on.

This is mostly used within subroutines, which expect an array among their parameters. Such subroutines tend to use the arraydim-function to check, if the array which has been passed, has the right dimension. E.g. a subroutine to multiply two matrices may want to check, if it really is invoked with two 2-dimensional arrays.

Example

dim a(10,10),b(10)
print arraydim(a()),arraydim(b())
          

This will print 2 1, which are the dimension of the arrays a() and b(). You may check out the function arraysize for a full example.

See also

arraysize and dim.


Name

arraysize() — returns the size of a dimension of an array

Synopsis

x=arraysize(a(),b)

Description

The arraysize-function computes the size of the specified dimension of a given array. Here, size stands for the maximum number, that may be used as an index for this array. The first argument to this function must be an reference to an array, the second one specifies, which of the multiple dimensions of the array should be taken to calculate the size.

An Example involving subroutines: Let's say, an array has been declared as dim a(10,20) (that is a two-dimensional array or a matrix). If this array is passed as an array reference to a subroutine, this sub will not know, what sort of array has been passed. With the arraydim-function the sub will be able to find the dimension of the array, with the arraysize-function it will be able to find out the size of this array in its two dimensions, which will be 10 and 20 respectively.

Our sample array is two dimensional; if you envision it as a matrix this matrix has 10 lines and 20 columns (see the dim-statement above. To state it more formally: The first dimension (lines) has a size of 10, the second dimension (columns) has a size of 20; these numbers are those returned by arraysize(a(),1) and arraysize(a(),2) respectively. Refer to the example below for a typical usage.

Example


rem
rem  This program adds two matrices elementwise.
rem

dim a(10,20),b(10,20),c(10,20)

rem  initialization of the arrays a() and b() 
for y=1 to 10:for x=1 to 20
   a(y,x)=int(ran(4)):b(y,x)=int(ran(4))
next x:next y

matadd(a(),b(),c())

print "Result:"
for x=1 to 20
   for y=10 to 1 step -1
      print c(y,x)," ";
   next y
   print
next x

sub matadd(m1(),m2(),r())

   rem  This sub will add the matrices m1() and m2()
   rem  elementwise and store the result within r()
   rem  This is not very useful but easy to implement.
   rem  However, this sub excels in checking its arguments
   rem  with arraydim() and arraysize()

   local x:local y
   
   if (arraydim(m1())<>2 or arraydim(m2())<>2 or arraydim(r())<>2) then
      error "Need two dimensional arrays as input"
   endif

   y=arraysize(m1(),1):x=arraysize(m1(),2)
   if (arraysize(m2(),1)<>y or arraysize(m2(),2)<>x) then
      error "The two matrices cannot be added elementwise"
   endif

   if (arraysize(r(),1)<>y or arraysize(r(),2)<>x) then
      error "The result cannot be stored in the third argument"
   endif

   local xx:local yy
   for xx=1 to x
      for yy=1 to y
         r(yy,xx)=m1(yy,xx)+m2(yy,xx)
      next yy
   next xx

 end sub

          

See also

arraydim and dim.


Name

asc() — accepts a string and returns the position of its first character within the ascii charset

Synopsis

a=asc(char$)

Description

The asc-function accepts a string, takes its first character and looks it up within the ascii-charset; this position will be returned. The asc-function is the opposite of the chr$-function. There are valid uses for asc, however, comparing strings (i.e. to bring them into alphabetical sequence) is not among them; in such many cases you might consider to compare strings directly with <, = and > (rather than converting a string to a number and comparing this number).

Example

input "Please enter a letter between 'a' and 'y': " a$
if (a$<"a" or a$>"y") print a$," is not in the proper range":end
print "The letter after ",a$," is ",chr$(asc(a$)+1)
          

See also

chr$


Name

asin() — returns the arcus sine of its numeric argument

Synopsis

angle=asin(x)

Description

acos is the arcus sine-function, i.e. the inverse of the sin-function. Or, more elaborate: It Returns the angle (in radians, not degrees !), which, fed to the sine-function will produce the argument passed to the asin-function.

Example

print asin(0.5),asin(sin(pi))
          

This will print 0.523599 -2.06823e-13 which is π/6 and almost 0 respectively.

See also

sin, acos


Name

at() — can be used in the print-command to place the output at a specified position

Synopsis

clear screen
…
print at(a,b)
print @(a,b)

Description

The at-clause takes two numeric arguments (e.g. at(2,3)) and can be inserted after the print-keyword. at() can be used only if clear screen has been executed at least once within the program (otherwise you will get an error).

The two numeric arguments of the at-function may range from 0 to the width of your terminal minus 1, and from 0 to the height of your terminal minus 1; if any argument exceeds these values, it will be truncated accordingly. However, yabasic has no influence on the size of your terminal (80x25 is a common, but not mandatory), the size of your terminal and the maximum values acceptable within the at-clause may vary. To get the size of your terminal you may use the peek-function: peek("screenwidth") returns the width of your terminal and peek("screenheight") its height.

Example

clear screen
maxx=peek("screenwidth")-1:maxy=peek("screenheight")-1
for x=0 to maxx
  print at(x,maxy*(0.5+sin(2*pi*x/maxx)/2)) "*"
next x
          

This example plots a full period of the sine-function across the screen.


Name

atan() — returns the arctangent of its numeric argument

Synopsis

angle=atan(a,b)
angle=atan(a)

Description

atan is the arctangent-function, i.e. the inverse of the tan-function. Or, more elaborate: It Returns the angle (in radians, not degrees !), which, fed to the tan-function will produce the argument passed to the atan-function.

The atan-function has a second form, which accepts two arguments: atan(a,b) which is (mostly) equivalent to atan(a/b) except for the fact, that the two-argument-form returns an angle in the range -π to π, whereas the one-argument-form returns an angle in the range -π/2 to π/2. To understand this you have to be good at math.

Example

print atan(1),atan(tan(pi)),atan(-0,-1),atan(-0,1)
          

This will print 0.463648 2.06823e-13 -3.14159 3.14159 which is π/4, almost 0, -π and π respectively.

See also

tan, sin

B

backcolor — change color for background of graphic window
beep — ring the bell within your computer; a synonym for bell
bell — ring the bell within your computer (just as beep)
bin$() — converts a number into a sequence of binary digits
bind() — binds a yabasic-program and the yabasic-interpreter together into a standalone program
bitnot() — the bitwise arithmetic not
box — draw a rectangle. A synonym for rectangle
break — breaks out of one or more loops or switch statements

Name

color — change color for background of graphic window

Synopsis

backcolour red,green,blue
backcolour "red,green,blue"
	  

Description

Change the color, that becomes visible, if any portion of the window is erased, e.g. after clear window or clear line. Note however, that parts of the window, that show the old background color will not change.

As with the color-command, the new background color can either be specified as a triple of three numbers or as a single string, that contains those three numbers separated by commas.

Note, that the command backcolor can be written as backcolour too and vice versa.

Example

open window 255,255
for x=10 to 235 step 10:for y=10 to 235 step 10
  	backcolour x,y,0
	clear window
	sleep 1
next y:next x
            

This changes the background colour of the graphic window repeatedly and clears it every time, so that it is filled with the new background colour.


Name

beep — ring the bell within your computer; a synonym for bell

Synopsis

beep

Description

The bell-command rings the bell within your computer once. This command is not a sound-interface, so you can neither vary the length or the height of the sound (technically, it just prints \a). bell is exactly the same as beep.

Example

beep:print "This is a problem ..."
          

See also

beep


Name

bell — ring the bell within your computer (just as beep)

Synopsis

bell

Description

The beep-command rings the bell within your computer once. beep is a synonym for bell.

Example

print "This is a problem ...":beep
          

See also

bell


Name

bin$() — converts a number into a sequence of binary digits

Synopsis

hexadecimal$=bin$(decimal)

Description

The bin$-function takes a single numeric argument an converts it into a string of binary digits (i.e. zeroes and ones). If you pass a negative number to bin$, the resulting string will be preceded by a '-'.

If you want to convert the other way around (i.e. from binary to decimal) you may use the dec-function.

Example

for a=1 to 100
  print bin$(a)
next a
          

This example prints the binary representation of all digits between 1 and 100.


Name

bind() — binds a yabasic-program and the yabasic-interpreter together into a standalone program

Synopsis

bind("foo.exe")

Description

The bind-command combines your own yabasic-program (plus all the libraries it does import) and the interpreter by copying them into a new file, whose name is passed as an argument. This new program may then be executed on any computer, even if it does not have yabasic installed.

Please see the section about creating a standalone-program for details.

Example

if (!peek("isbound")) then
  bind "foo"
  print "Successfully created the standalone executable 'foo' !"
  exit
endif

print "Hello World !"
          

This example creates a standalone program foo from itself.

See also

The section about creating a standalone-program, the peek-function and the command line options.


Name

bitnot() — the bitwise arithmetic not

Synopsis

x=bitnot(a)

Description

This function is used to compute the bitwise not of its single argument. The argument is treated as binary number (i.e. a sequence of digits 0 and 1); a bit of the resulting value will be 1, if the argument has a 0 at this position in its binary representation; if the bit in the argument is 1, the bit in the result will be 0.

Note, that its argument is silently converted to a positive integer value and that negative numbers have their own binary representation and may lead to unexpected results when passed to bitnot.

A note on naming: This one-argument-function is named bitnot to distinguish it from the one-argument-function not, which operates on logical expressions. For the similar functions and and or this distinction between logical and bitwise function is done implicitly through the number of arguments (1 and 2, respectively).

Example

print bin$(not(17))
          

This will print 11111111111111111111111111101110. This result is clear, if you note, that the binary representation of 17 is 10001, which inverted will give the long binary number given before.

See also

or, eor and and


Name

box — draw a rectangle. A synonym for rectangle

Synopsis

See the rectangle-command.

Description

The box-command does exactly the same as the rectangle-command; it is just a synonym. Therefore you should refer to the entry for the rectangle-command for further information.


Name

break — breaks out of one or more loops or switch statements

Synopsis

break
break 2

Description

break transfers control immediately outside the enclosing loop or switch statement. This is the preferred way of leaving a such a statement (rather than goto, which is still possible in most cases). An optional digit allows one to break out of multiple levels, e.g. to leave a loop from within a switch statement. Please note, that only a literal (e.g. 2) is allowed at this location.

Example

for a=1 to 10
  break
  print "Hi"
next a

while 1
  break
  print "Hi"
wend

repeat
  break
  print "Hi"
until 0

switch 1
case 1:break
case 2:case 3:print "Hi"
end switch
          

This example prints nothing at all, because each of the loops (and the switch-statement) does an immediate break (before it could print any "Hi").

See also

for, while, repeat and switch.

C

case — mark the different cases within a switch-statement
ceil() — compute the ceiling for its (float) argument
chomp$() — remove a single trailing newline from its string-argument; if the string does not end in a newline, the string is returned unchanged
chr$() — accepts a number and returns the character at this position within the ascii charset
circle — draws a circle in the graphic-window
clear — erase circles, rectangles or triangles
clear screen — erases the text window
clear window — clear the graphic window and begin a new page, if printing is under way
close — close a file, which has been opened before
close curve — close a curve, that has been drawn by the line-command
close printer — stops printing of graphics
close window — close the graphics-window
color — change color for any subsequent drawing-command
compile — compile a string with yabasic-code on the fly
continue — start the next iteration of a for-, do-, repeat- or while-loop
cos() — return the cosine of its single argument

Name

case — mark the different cases within a switch-statement

Synopsis

switch a
  case 1
  case 2
  …
end switch

…

switch a$
  case "a"
  case "b"
  …
end switch

Description

Please see the switch-statement.

Example

input a
switch(a)
  case 1:print "one":break
  case 2:print "two":break
  default:print "more"
end switch
          

Depending on your input (a number is expected) this code will print one or two or otherwise more.

See also

switch


Name

ceil() — compute the ceiling for its (float) argument

Synopsis

print ceil(x)

Description

The ceil-function returns the smallest integer number, that is larger or equal than its argument.

Example

print ceil(1.5),floor(1.5)
print ceil(2),floor(2)
          

Comparing functions ceil and floor, gives a first line of output (1 2), showing that ceil is less or equal than floor; but as the second line of output (2 2) shows, the two functions give equal results for integer arguments.

See also

floor, int, frac, round


Name

chomp$() — remove a single trailing newline from its string-argument; if the string does not end in a newline, the string is returned unchanged

Synopsis

print chomp$("Hallo !\n")

Description

The chomp$-function checks, if its string-argument ends in a newline and removes it eventually; for this purpose chomp$ can replace an if-statement. This can be especially useful, when you deal with input from external sources like system$.

You may apply chomp$ freely, as it only acts, if there is a newline to remove; note however, that user-input, that comes from the normal input-statement, does not need such a treatment, because it already comes without a newline.

Example

The following yabasic-program uses the unix-command whoami to get the username of the current user in order to greet him personally. This is done twice: First with the chomp$-function and then again with with an equivalent if-statement:

print "Hello " + chomp$(system$("whoami")) + " !"

user$ = system$("whoami")
if (right$(user$,1)="\n") user$=left$(user$,len(user$)-1)
print "Hello again " + user$ + " !"
          

See also

system$


Name

chr$() — accepts a number and returns the character at this position within the ascii charset

Synopsis

character$=chr$(ascii)

Description

The chr$-function is the opposite of the asc-function. It looks up and returns the character at the given position within the ascii-charset. It's typical use is to construct nonprintable characters which do not occur on your keyboard.

Nevertheless you won't use chr$ as often as you might think, because the most important nonprintable characters can be constructed using escape-sequences using the \-character (e.g. you might use \n instead of chr$(10) wherever you want to use the newline-character).

Example

print "a",chr$(10),"b"
          

This will print the letters 'a' and 'b' in different lines because of the intervening newline-character, which is returned by chr$(10).

See also

asc


Name

circle — draws a circle in the graphic-window

Synopsis

circle x,y,r
clear circle x,y,r
fill circle x,y,r
clear fill circle x,y,r

Description

The circle-command accepts three parameters: The x- and y-coordinates of the center and the radius of the circle.

Some more observations related with the circle-command:

  • The graphic-window must have been opened already.

  • The circle may well extend over the boundaries of the window.

  • If you have issued open printer before, the circle will finally appear in the printed hard copy of the window.

  • fill circle will draw a filled (with black ink) circle.

  • clear circle will erase (or clear) the outline of the circle.

  • clear fill circle or fill clear circle will erase the full area of the circle.

Example

open window 200,200

for n=1 to 2000
  x=ran(200)
  y=ran(200)
  fill circle x,y,10
  clear fill circle x,y,8
next n
          

This code will open a window and draw 2000 overlapping circles within. Each circle is drawn in two steps: First it is filled with black ink (fill circle x,y,10), then most of this circle is erased again (clear fill circle x,y,8). As a result each circle is drawn with an opaque white interior and a 2-pixel outline (2-pixel, because the radii differ by two).


Name

clear — erase circles, rectangles or triangles

Synopsis

clear rectangle 10,10,90,90
clear fill circle 50,50,20
clear triangle 10,10,20,20,50,30

Description

May be used within the circle, rectangle or triangle command and causes these shapes to be erased (i.e. be drawn in the colour of the background).

fill can be used in conjunction with and wherever the fill-clause may appear. Used alone, clear will erase the outline (not the interior) of the shape (circle, rectangle or triangle); together with fill the whole shape (including its interior) is erased.

Example

open window 200,200
fill circle 100,100,50
clear fill rectangle 10,10,90,90
          

This opens a window and draws a pacman-like figure.


Name

clear screen — erases the text window

Synopsis

clear screen

Description

clear screen erases the text window (the window where the output of print appears).

It must be issued at least once, before some advanced screen-commands (e.g. print at or inkey$) may be called; this requirement is due to some limitations of the curses-library, which is used by yabasic under Unix for some commands.

Example

clear screen
print "Please press a key : ";
a$=inkey$
print a$
          

The clear screen command is essential here; if it would be omitted, yabasic would issue an error ("need to call 'clear screen' first") while trying to execute the inkey$-function.

See also

inkey$


Name

clear window — clear the graphic window and begin a new page, if printing is under way

Synopsis

clear window

Description

clear window clears the graphic window. If you have started printing the graphic via open printer, the clear window-command starts a new page as well.

Example

open window 200,200
open printer "t.ps"

for a=1 to 10
if (a>1) clear window
text 100,100,"Hallo "+str$(a)
next a

close printer
close window
          

This example prints 10 pages, with the text "Hello 1", "Hello 2", … and so on. The clear screen-command clears the graphics window and starts a new page.


Name

close — close a file, which has been opened before

Synopsis

close filenum
close # filenum

Description

The close-command closes an open file. You should issue this command as soon as you are done with reading from or writing to a file.

Example

open "my.data" for reading as 1
input #1 a
print a
close 1
          

This program opens the file "my.data", reads a number from it, prints this number and closes the file again.

See also

open


Name

close curve — close a curve, that has been drawn by the line-command

Synopsis

new curve
line to x1,y1
…
close curve

Description

The close curve-command closes a sequence of lines, that has been drawn by repeated line to-commands.

Example

open window 200,200
new curve
line to 100,50
line to 150,150
line to 50,150
close curve
          

This example draws a triangle: The three line to-commands draw two lines; the final line is however not drawn explicitly, but drawn by the close curve-command.

See also

line, new curve


Name

close printer — stops printing of graphics

Synopsis

close printer

Description

The close printer-command ends the printing graphics. Between open printer and close printer everything you draw (e.g. circles, lines …) is sent to your printer. close printer puts an end to printing and will make your printer eject the page.

Example

open window 200,200
open printer
circle 100,100,50
close printer
close window
          

As soon as close printer is executed, your printer will eject a page with a circle on it.

See also

open printer


Name

close window — close the graphics-window

Synopsis

close window

Description

The close window-command closes the graphics-window, i.e. it makes it disappear from your screen. It includes an implicit close printer, if a printer has been opened previously.

Example

open window 200,200
circle 100,100,50
close window
          

This example will open a window, draw a circle and close the window again; all this without any pause or delay, so the window will be closed before you may regard the circle..

See also

open window


Name

color — change color for any subsequent drawing-command

Synopsis

colour red,green,blue
colour "red,green,blue"

Description

Change the color, in which lines, dots, circles, rectangles or triangles are drawn. The color-command accepts three numbers in the range 0 … 255 (as in the first line of the synopsis above). Those numbers specify the intensity for the primary colors red, green and blue respectively. As an example 255,0,0 is red and 255,255,0 is yellow.

Alternatively you may specify the color with a single string (as in the second line of the synopsis above); this string should contain three numbers, separated by commas. As an example "255,0,255" would be violet. Using this variant of the colour-command, you may use symbolic names for colours:

open window 100,100
yellow$="255,255,0"
color yellow$
text 50,50,"Hallo"
	  

, which reads much clearer.

Example

open window 255,255
for x=10 to 235 step 10:for y=10 to 235 step 10
  	colour x,y,0
  	fill rectangle x,y,x+10,y+10
next y:next x
            

This fills the window with colored rectangles. However, none of the used colours contains any shade of blue, because the color-command has always 0 as a third argument.

Note, that the command color can be written as colour too and vice versa.


Name

compile — compile a string with yabasic-code on the fly

Synopsis

compile(code$)

Description

This is an advanced command (closely related with the execute-command). It allows you to compile a string of yabasic-code (which is the only argument). Afterwards the compiled code is a normal part of your program.

Note, that there is no way to remove the compiled code.

Example

compile("sub mysub(a):print a:end sub")
mysub(2)
          

This example creates a function named mysub, which simply prints its single argument.

See also

execute


Name

continue — start the next iteration of a for-, do-, repeat- or while-loop

Synopsis

continue

Description

You may use continue within any loop to start the next iteration immediately. Depending on the type of the loop, the loop-condition will or will not be checked. Especially: for- and while-loops will evaluate their respective conditions, do- and repeat-loops will not.

Remark: Another way to change the flow of execution within a loop, is the break-command.

Example

for a=1 to 100
  if mod(a,2)=0 continue
  print a
next a
          

This example will print all odd numbers between 1 and 100.

See also

for, do, repeat, while, break


Name

cos() — return the cosine of its single argument

Synopsis

x=cos(angle)

Description

The cos-function expects an angle (in radians) and returns its cosine.

Example

print cos(pi)
          

This example will print -1.

See also

acos, sin

D

data — introduces a list of data-items
date$ — returns a string with various components of the current date
dec() — convert a base 2 or base 16 number into decimal form
default — mark the default-branch within a switch-statement
dim — create an array prior to its first use
do — start a (conditionless) do-loop
doc — special comment, which might be retrieved by the program itself
docu$ — special array, containing the contents of all docu-statement within the program
dot — draw a dot in the graphic-window

Name

data — introduces a list of data-items

Synopsis

data 9,"world"
…
read b,a$

Description

The data-keyword introduces a list of comma-separated list of strings or numbers, which may be retrieved with the read-command.

The data-command itself does nothing; it just stores data. A single data-command may precede an arbitrarily long list of values, in which strings or numbers may be mixed at will.

yabasic internally uses a data-pointer to keep track of the current location within the data-list; this pointer may be reset with the restore-command.

Example

do
  restore
  for a=1 to 4
    read num$,num
    print num$,"=",num
  next a
loop
data "eleven",11,"twelve",12,"thirteen",13,"fourteen",14
          

This example just prints a series of lines eleven=11 up to fourteen=14 and so on without end.

The restore-command ensures that the list of data-items is read from the start with every iteration.

See also

read, restore


Name

date$ — returns a string with various components of the current date

Synopsis

a$=date$

Description

The date$-function (which must be called without parentheses; i.e. date$() would be an error) returns a string containing various components of a date; an example would be 4-05-27-2004-Thu-May. This string consists of various fields separated by hyphens ("-"):

  • The day within the week as a number in the range 0 (=Sunday) to 6 (=Saturday) (in the example above: 4, i.e. Thursday).

  • The month as a number in the range 1 (=January) to 12 (=December) (in the example: 5 which stands for May).

  • The day within the month as a number in the range 1 to 31 (in the example: 27).

  • The full, 4-digit year (in the example: 2004, which reminds me that I should adjust the clock within my computer …).

  • The abbreviated name of the day within the week (Mon to Sun).

  • The abbreviated name of the month (Jan to Dec).

Therefore the whole example above (4-05-27-2004-Thu-May) would read: day 4 in the week (counting from 0), May 27 in the year 2004, which is a Thursday in May.

Note, that all fields within the string returned by date$ have a fixed with (numbers are padded with zeroes); therefore it is easy to extract the various fields of a date format with mid$.

Example

rem   Two ways to print the same ...

print mid$(date$,3,10)

dim fields$(6)
a=split(date$,fields$(),"-")
print fields$(2),"-",fields$(3),"-",fields$(4)
          

This example shows two different techniques to extract components from the value returned by date$. The mid$-function is the preferred way, but you could just as well split the return-value of date$ at every "-" and store the result within an array of strings.

See also

time$


Name

dec() — convert a base 2 or base 16 number into decimal form

Synopsis

a=dec(number$)
a=dec(number$,base)

Description

The dec-function takes the string-representation of a base-2 or base-16 (which is the default) number and converts it into a decimal number. The optional second argument (base) might be used to specify a base other than 16. However, currently only base 2 or base 16 are supported. Please note, that for base 16 and 2 you may write literals in the usual way, by preceding them with 0x or 0b respectively, e.g. like

print 0xff + 0b11

; this may save you from applying the dec altogether.

Example

input "Please enter a binary number: " a$
print a$," is ",dec(a$)
          

Name

default — mark the default-branch within a switch-statement

Synopsis

switch a+3
case 1
  …
case 2
  …
default
  …
end switch

Description

The default-clause is an optional part of the switch-statement (see there for more information). It introduces a series of statements, that should be executed, if none of the cases matches, that have been specified before (each with its own case-clause).

So default specifies a default to be executed, if none of the explicitly named cases matches; hence its name.

Example

print "Please enter a number between 0 and 6,"
print "specifying a day in the week."
input d
switch d
case 0:print "Monday":break
case 1:print "Tuesday":break
case 2:print "Wednesday":break
case 3:print "Thursday":break
case 4:print "Friday":break
case 5:print "Saturday":break
case 6:print "Sunday":break
default:print "Hey you entered something invalid !"
end switch
          

This program translates a number between 0 and 6 into the name of a weekday; the default-case is used to detect (and complain about) invalid input.

See also

sub, case


Name

dim — create an array prior to its first use

Synopsis

dim array(x,y)
dim array$(x,y)

Description

The dim-command prepares one or more arrays (of either strings or numbers) for later use. This command can also be used to enlarges an existing array.

When an array is created with the dim-statement, memory is allocated and all elements are initialized with either 0 (for numerical arrays) or "" (for string arrays).

If the array already existed, and the dim-statement specifies a larger size than the current size, the array is enlarged and any old content is preserved.

Note, that dim cannot be used to shrink an array: If you specify a size, that is smaller than the current size, the dim-command does nothing.

Finally: To create an array, that is only known within a single subroutine, you should use the command local, which creates local variables as well as local arrays.

Example

dim a(5,5)
for x=1 to 5:for y=1 to 5
  a(x,y)=int(ran(100))
next y:next x
printmatrix(a())
dim a(7,7)
printmatrix(a())

sub printmatrix(ar())
  local x,y,p,q
  x=arraysize(ar(),1)
  y=arraysize(ar(),2)
  for q=1 to y
    for p=1 to y
      print ar(p,q),"\t";
    next p
    print
  next q
end sub
          

This example creates a 2-dimensional array (i.e. a matrix) with the dim-statement and fills it with random numbers. The second dim-statement enlarges the array, all new elements are filled with 0.

The subroutine printmatrix just does, what its name says.


Name

do — start a (conditionless) do-loop

Synopsis

do 
… 
loop

Description

Starts a loop, which is terminated by loop; everything between do and loop will be repeated forever. This loop has no condition, so it is an infinite loop; note however, that a break- or goto-statement might be used to leave this loop anytime.

Example

do
  a=a+1
  print a
  if (a>100) break
loop
          

This example prints the numbers between 1 and 101. The break-statement is used to leave the loop.

See also

loop, repeat, while, break


Name

doc — special comment, which might be retrieved by the program itself

Synopsis

doc   This is a comment
docu  This is another comment

Description

Introduces a comment, which spans up to the end of the line. But other than the rem-comment, any docu-comment is collected within the special docu$-array and might be retrieved later on. Moreover you might invoke yabasic -docu foo.yab on the command line to retrieve the embedded documentation within the program foo.yab.

Instead of doc you may just as well write docu or even documentation.

Example

rem   Hi, this has been written by me
rem
doc   This program asks for a number and
doc   prints this number multiplied with 2
rem
rem   Print out the above message
rem
for a=1 to arraysize(docu$(),1):print docu$(a):next a

rem   Read and print the number
input "Please input a number: " x
print x*2
          

This program uses the comments within its code to print out a help message for the user; if you run this program, you get this output:

  This program asks for a number and
  prints this number multiplied with 2
Please input a number: 2
4

The contents of the doc-lines are retrieved from the docu$-array; if you do not want a comment to be collected within this array, use the rem-statement instead.

See also

docu$, rem


Name

docu$ — special array, containing the contents of all docu-statement within the program

Synopsis

a$=docu$(1)

Description

Before your program is executed, yabasic collects the content of all the doc-statements within your program within this 1-dimensional array (well only those within the main-program, libraries are skipped).

You may use the arraysize function to find out, how many lines it contains.

Example

docu
docu  This program reads two numbers 
docu  and adds them.
docu

rem retrieve and print the embedded documentation
for a=1 to arraysize(docu$(),1)
  print docu$(a)
next a

input "First number: " b
input "Second number: " c

print "The sum of ",b," and ",c," is ",b+c
          

This program uses the embedded documentation to issue a usage-message.

See also

arraydim, rem


Name

dot — draw a dot in the graphic-window

Synopsis

dot x,y
clear dot x,y

Description

Draws a dot at the specified coordinates within your graphic-window. If printing is in effect, the dot appears on your printout too.

Use the functions peek("winheight") or peek("winwidth") to get the size of your window and hence the boundaries of the coordinates specified for the dot-command.

Example

open window 200,200
circle 100,100,100
do
  x=ran(200):y=ran(200)
  dot x,y
  total=total+1
  if (sqrt((x-100)^2+(y-100)^2)<100) in=in+1
  print 4*in/total
loop
          

This program uses a well known algorithm to compute π.

See also

line, open window

E

else — mark an alternative within an if-statement
elsif — starts an alternate condition within an if-statement
end — terminate your program
endif — ends an if-statement
end sub — ends a subroutine definition
eof — check, if an open file contains data
eor() — compute the bitwise exclusive or of its two arguments
error — raise an error and terminate your program
euler — another name for the constant 2.71828182864
execute$() — execute a user defined subroutine, which must return a string
execute() — execute a user defined subroutine, which must return a number
exit — terminate your program
exp() — compute the exponential function of its single argument
export — mark a function as globally visible

Name

else — mark an alternative within an if-statement

Synopsis

if (…) then 
  … 
else 
  … 
endif

Description

The else-statement introduces the alternate branch of an if-statement. I.e. it starts the sequence of statements, which is executed, if the condition of the if-statement is not true.

Example

input "Please enter a number: " a
if (mod(a,2)=1) then
  print a," is odd."
else
  print a," is even."
endif
          

This program detects, if the number you have entered is even or odd.

See also

if


Name

elsif — starts an alternate condition within an if-statement

Synopsis

if (…) then
  …
elseif (…) 
  …
elsif (…) then
  …
else
  …
endif

Description

The elsif-statement is used to select a single alternative among a series of choices.

With each elsif-statement you may specify a condition, which is tested, if the main condition (specified with the if-statement) has failed. Note that elsif might be just as well written as elseif.

Within the example below, two variables a and b are tested against a range of values. The variable a is tested with the elsif-statement. The very same tests are performed for the variable b too; but here an involved series of if-else-statements is employed, making the tests much more obscure.

Example

input "Please enter a number: " a
if (a<0) then
  print "less than 0"
elseif (a<=10) then
  print "between 0 and 10"
elsif (a<=20)
  print "between 11 and 20"
else
  print "over 20"
endif

input "Please enter another number: " b
if (b<0) then
  print "less than 0"
else
  if (b<=10) then
    print "between 0 and 10"
  else
    if (b<=20) then
      print "between 11 and 20"
    else
      print "over 20"
    endif
  endif
endif
          

Note, that the very same tests are performed for the variables a and b, but can be stated much more clearly with the elsif-statement.

Note, that elsif might be written as elseif too, and that the keyword then is optional.

See also

if, else


Name

end — terminate your program

Synopsis

end

Description

Terminate your program. Much (but not exactly) like the exit command.

Note, that end may not end your program immediately; if you have opened a window or called clear screen, yabasic assumes, that your user wants to study the output of your program after it has ended; therefore it issues the line ---Program done, press RETURN--- and waits for a key to be pressed. If you do not like this behaviour, consider using exit.

Example

print "Do you want to continue ?"
input "Please answer y(es) or n(o): " a$
if (lower$(left$(a$,1))="n") then
  print "bye"
  end
fi
          

See also

exit


Name

endif — ends an if-statement

Synopsis

if (…) then
  …
endif

Description

The endif-statement closes (or ends) an if-statement.

Note, that endif may be written in a variety of other ways: end if, end-if or even fi.

The endif-statement must be omitted, if the if-statement does not contain the keyword then (see the example below). Such an if-statement without endif extends only over a single line.

Example

input "A number please: " a
if (a<10) then
  print "Your number is less than 10."
endif

REM  and now without endif 

input "A number please: " a
if (a<10) print "Your number is less than 10."
          

See also

if


Name

end sub — ends a subroutine definition

Synopsis

sub foo(…) 
  …
end sub

Description

Marks the end of a subroutine-definition (which starts with the sub-keyword). The whole concept of subroutines is explained within the entry for sub.

Example

print foo(3)

sub foo(a)
  return a*2
end sub
          

This program prints out 6. The subroutine foo simply returns twice its argument.

See also

sub


Name

eof — check, if an open file contains data

Synopsis

open 1,"foo.bar"
if (eof(1)) then 
   …
end if

Description

The eof-function checks, if there is still data left within an open file. As an argument it expects the file-number as returned by (or used within) the open-function (or statement).

Example

a=open("foo.bar")
while not eof(a)
  input #a,a$
  print a$
end while
          

This example will print the contents of the file "foo.bar". The eof-function will terminate the loop, if there is no more data left within the file.

See also

open


Name

eor() — compute the bitwise exclusive or of its two arguments

Synopsis

print eor(a,b)

Description

The eor-function takes two arguments and computes their bitwise exclusive or. I.e. treat each arguments as a sequence of bits and compare theses two sequences bit by bit to produce the result. If the bits from the arguments are equal, the resulting bit will be 0, otherwise 1.

The xor-function is the same as the eor function; both are synonymous; however they have each their own description, so you may check out the entry of xor for a slightly different view.

Example

for a=0 to 3
  for b=0 to 3
    print fill$(bin$(a))," eor ",fill$(bin$(b))," = ",fill$(bin$(eor(a,b)))
  next b
next a

sub fill$(a$)
  return right$("0"+a$,2)
end sub
          

This example prints a table, from which you may figure, how the eor-function is computed.

See also

and, or


Name

error — raise an error and terminate your program

Synopsis

error "Wrong, wrong, wrong !!"

Description

Produces the same kind or error messages, that yabasic itself produces (e.g. in case of a syntax-error). The single argument is issued along with the current line-number.

Example

input "Please enter a number between 1 and 10: " a
if (a<1 or a>10) error "Oh no ..."
          

This program is very harsh in checking the users input; instead of just asking again, the program terminates with an error, if the user enters something wrong.

The error message would look like this:

---Error in t.yab, line 2: Oh no ...
---Error: Program stopped due to an error

See also

Well, there should be a corresponding called warning; unfortunately ther is none yet.


Name

euler — another name for the constant 2.71828182864

Synopsis

foo=euler

Description

euler is the well known constant named after Leonard Euler; its value is 2.71828182864. euler is not a function, so parens are not allowed (i.e. euler() will produce an error). Finally, you may not assign to euler; it wouldn't sense anyway, because it is a constant.

Example

print euler
          

See also

pi


Name

execute$() — execute a user defined subroutine, which must return a string

Synopsis

print execute$("foo$","arg1","arg2")

Description

execute$ can be used to execute a user defined subroutine, whose name may be specified as a string expression.

This feature is the only way to execute a subroutine, whose name is not known by the time you write your program. This might happen, if you want to execute a subroutine, which is compiled (using the compile command) during the course of execution of your program.

Note however, that the execute$-function is not the preferred method to execute a user defined subroutine; in almost all cases you should just execute a subroutine by writing down its name within your yabasic program (see the example below).

Example

print execute$("foo$","Hello","world !")
sub foo$(a$,b$)
  return a$+" "+b$
end sub
          

The example simply prints Hello world !, which is the return value of the user defined subroutine foo$. The same could be achieved by executing:

print foo$(a$,b$)

See also

compile, execute


Name

execute() — execute a user defined subroutine, which must return a number

Synopsis

print execute("bar","arg1","arg2")

Description

The execute-function is the counterpart of the execute$-function (please see there for some caveats). execute executes subroutines, which returns a number.

Example

print execute("bar",2,3)
sub bar(a,b)
  return a+b
end sub
          

See also

compile, execute$


Name

exit — terminate your program

Synopsis

exit
exit 1

Description

Terminate your program and return any given value to the operating system. exit is similar to end, but it will terminate your program immediately, no matter what.

Example

print "Do you want to continue ?"
input "Please answer y(es) or n(o): " a$
if (lower$(left$(a$,1))="n") exit 1
          

See also

end


Name

exp() — compute the exponential function of its single argument

Synopsis

foo=exp(bar)

Description

This function computes e to the power of its argument, where e is the well known euler constant 2.71828182864.

The exp-function is the inverse of the log-function.

Example

open window 100,100
for x=0 to 100
   dot x,100-100*exp(x/100)/euler
next x
          

This program plots part of the exp-function, however the range is rather small, so that you may not recognize the function from this plot.

See also

log


Name

export — mark a function as globally visible

Synopsis

export sub foo(bar)
…
end sub

Description

The export-statement is used within libraries to mark a user defined subroutine as visible outside the library wherein it is defined. Subroutines, which are not exported, must be qualified with the name of the library, e.g. foo.baz (where foo is the name of the library and baz the name of the subroutine); exported subroutines may be used without specifying the name of the library, e.g. bar.

Therefore export may only be useful within libraries.

Example

The library foo.bar (which is listed below) defines two functions bar and baz, however only the function bar is exported and therefore visible even outside the library; baz is not exported and may only be used within the library foo.yab:

export sub bar()
  print "Hello"
end sub

sub baz()
  print "World"
end sub
          

Now within your main program cux.yab (which imports the library foo.yab); note that this program produces an error:

import foo

print "Calling subroutine foo.bar (okay) ..."
foo.bar()
print "done."

print "Calling subroutine bar (okay) ..."
bar()
print "done."

print "Calling subroutine foo.baz (okay) ..."
foo.baz()
print "done."

print "Calling subroutine baz (NOT okay) ..."
baz()
print "done."

The output when executing yabasic foo.yab is this:

Calling subroutine foo.bar (okay) ...
Hello
done.
Calling subroutine bar (okay) ...
Hello
done.
Calling subroutine foo.baz (okay) ...
World
done.
Calling subroutine baz (NOT okay) ...
---Error in main.yab, line 16: can't find subroutine 'baz'
---Dump: sub baz() called in main.yab,16
---Error: Program stopped due to an error

As the error message above shows, the subroutine baz must be qualified with the name of the library, if used outside the library, wherein it is defined (e.g. foo.baz. I.e. outside the library foo.yab you need to write foo.baz. baz alone would be an error.

The subroutine bar (without adding the name of the library) however may (and probably should) be used in any program, which imports the library foo.yab.

Note

In some sense the set of exported subroutines constitutes the interface of a library.

See also

sub, import

F

false — a constant with the value of 0
fi — another name for endif
fill — draw a filled circles, rectangles or triangles
floor() — compute the floor for its (float) argument
for — starts a for-loop
foreign_buffer_alloc$() — Create a new buffer for use in a foreign function call
foreign_buffer_dump$() — return the content of a buffer as a hex-encoded string
foreign_buffer_free — free a foreign buffer
foreign_buffer_get() — extract a number from a foreign buffer
foreign_buffer_get$() — extract a string from a foreign buffer
foreign_buffer_get_buffer$() — take a buffer and construct a handle to a second buffer from its content
foreign_buffer_set — store a given value within a buffer
foreign_buffer_set_buffer — store a pointer to one buffer within another buffer
foreign_buffer_size() — return the size of the foreign buffer
foreign_function_call() — call a function (returning a number) from a non-yabasic library or dll
foreign_function_call$() — call a function (returning a string or a buffer) from a non-yabasic library or dll
foreign_function_size() — return the size of one of the types available for foreign function calls
frnbf_ and frnfn_ — Abbreviations for foreign_buffer_ and foreign_function_
frac() — return the fractional part of its numeric argument

Name

false — a constant with the value of 0

Synopsis

okay=false

Description

The constant false can be assigned to variables which later appear in conditions (e.g. within an if-statement.

false may also be written as FALSE or even FaLsE.

Example

input "Please enter a number between 1 and 10: " a
if (check_input(a)) print "Okay"

sub check_input(x)
  if (x>10 or x<1) return false
  return true
end sub
          

The subroutine check_input checks its argument and returns true or false according to the outcome of the check..

See also

true


Name

fi — another name for endif

Synopsis

if (…)
…
fi

Description

fi marks the end of an if-statement and is exactly equivalent to endif, please see there for further information.

Example

input "A number please: " a
if (a<10) then
  print "Your number is less than 10."
fi
          

See also

endif


Name

fill — draw a filled circles, rectangles or triangles

Synopsis

fill rectangle 10,10,90,90
fill circle 50,50,20
fill triangle 10,20,20,10,20,20

Description

The keyword fill may be used within the circle, rectangle or triangle command and causes these shapes to be filled.

fill can be used in conjunction with and wherever the clear-clause may appear. Used alone, fill will fill the interior of the shape (circle, rectangle or triangle); together with clear the whole shape (including its interior) is erased.

Example

open window 200,200
fill circle 100,100,50
clear fill rectangle 10,10,90,90
          

This opens a window and draws a pacman-like figure.


Name

floor() — compute the floor for its (float) argument

Synopsis

print floor(x)

Description

The floor-function returns the largest integer number, that is smaller or equal than its argument. For positive numbers x, floor(x) is the same as int(x); for negaive numbers it can be different (see the example below).

Example

print int(-1.5),floor(-1.5)
print int(-1),floor(-1)
print int(1.5),floor(1.5)
          

This example compares the functions int and floor, starting with -1 -2, then -1 -1 and ending with 1 1, which shows the different behaviour of both functions.

See also

ceil, int, frac, round


Name

for — starts a for-loop

Synopsis

for a=1 to 100 step 2
  …
next a

Description

The for-loop lets its numerical variable (a in the synopsis) assume all values within the given range. The optional step-clause may specify a value (default: 1) by which the variable will be incremented (or decremented, if step is negative).

Any for-statement can be replaced by a set of ifs and gotos; as you may infer from the example below this is normally not feasible. However if you want to know in detail how the for-statement works, you should study this example, which presents a for-statement and an exactly equivalent series of ifs and gotos.

Example

for a=1 to 10 step 2:print a:next 

a=1
label check
if (a>10) goto done
  print a
  a=a+2
goto check
label done
          

This example simply prints the numbers 1, 3, 5, 7 and 9. It does this twice: First with a simple for-statement and then with ifs and gotos.

See also

step, next


Name

foreign_buffer_alloc$() — Create a new buffer for use in a foreign function call

Synopsis

handle$=foreign_buffer_alloc$(10)

Description

foreign_buffer_alloc$() creates a new buffer of specified size (using the C-function malloc). This buffer can then be populated by foreign_buffer_set or foreign_buffer_set_buffer, passed to foreign_function_call and finally freed with foreign_buffer_free.

The special value of -1 can be passed to create the equivalent of a null-pointer in C: when your yabasic-program passes such a buffer to an external function, it is replaced by a null-pointer.


Name

foreign_buffer_dump$() — return the content of a buffer as a hex-encoded string

Synopsis

	    print foreign_buffer_dump(handle$)

Description

foreign_buffer_dump$() is mostly used during development of your yabasic program and helps to investigate the content of a buffer; this can be helpful to find out, how a structure for a foreign function call is aggregated. To actually retrieve elements from the structure rather use foreign_buffer_get.


Name

foreign_buffer_free — free a foreign buffer

Synopsis

foreign_buffer_free handle$

Description

foreign_buffer_free() expects a handle for a buffer and frees this buffer (using the C-function free), i.e. gives this memory area back to the operating system. Any subsequent attempt to access part of this buffer (e.g. via foreign_buffer_get) will probably lead to an error (as will a second call to foreign_buffer_free()). The handle-argument must have been returned previously by foreign_buffer_alloc or foreign_function_call.


Name

foreign_buffer_get() — extract a number from a foreign buffer

Synopsis

print foreign_buffer_get(handle$,10,"int")

Description

foreign_buffer_get() retrieves a simple type from a buffer, that is assumed to contain a structure (see the overview-section for the necessary background). For this it needs three arguments:

  • A handle to a buffer, that has been previously filled, e.g. by a foreign function call.

  • An offset, counted in bytes from the start of the buffer, which specifies where the value can be found within the structure.

  • A string, specifying the type of the value that should be retrieved, which for this function is always an integer type like "int", "short" or "long".

Correct usage of this function requires an good understanding of the respective structure contained within the buffer.

See also

The overview-section on foreign functions, list of related functions and commands, the neighbouring functions for retrieving other values from the buffer.


Name

foreign_buffer_get$() — extract a string from a foreign buffer

Synopsis

print foreign_buffer_get$(handle$,0,12)

Description

foreign_buffer_get$() retrieves a string from a foreign buffer; its areguments are

  • A handle to a buffer, that has been previously filled, e.g. by a foreign function call.

  • An offset within this buffer, where the string starts. In the common case, where the buffer can be assumed to contain a string only, this offset should be 0.

  • The maximum length of the expected string. This is a value not necessarily known but if the string is null-terminated (as usual) you may just specify a much larger number here.

Correct usage of this function requires an good understanding of the respective structure contained within the buffer.


Name

foreign_buffer_get_buffer() — take a buffer and construct a handle to a second buffer from its content

Synopsis

handle2$ = foreign_buffer_get_buffer(handle$,8)

Description

foreign_buffer_get_buffer() should be used, if a buffer (i.e. the contained structure) is known to contain a pointer to a string or another structure. foreign_buffer_get_buffer() then reads this pointer and transforms it into a handle, that can then be used by other functions from the foreign_buffer_get-family. The two arguments are:

  • A handle to a buffer, that has been previously filled, e.g. by a foreign function call.

  • An offset within the buffer to the start of the buffer. A (third) length-argument is not required, because typically all pointers on a platform have the same length.

See the libcurl-example in the overview-section for an example.


Name

foreign_buffer_set — store a given value within a buffer

Synopsis

foreign_buffer_set handle$,4,"Hello World"
foreign_buffer_set handle$,6,"long",42

Description

foreign_buffer_set can be used to populate a structure within a foreign buffer. It accepts strings (first line in synopsis) and numbers (second line in synopsis) and stores them at the given offset. The arguments are:

  • A handle to a buffer, that might have been just allocated or been returned from a foreign function call.

  • An offset, specifying the first byte where the given data will be stored.

  • The third argument: If you want to store a string, specify it just here; if you want to store a number, specify its type (e.g. int).

  • A fourth argument is only needed, when you want to store a number; this number needs then to be given here.


Name

foreign_buffer_set_buffer — store a pointer to one buffer within another buffer

Synopsis

foreign_buffer_set handle1$,16,handle2$

Description

foreign_buffer_set_buffer stores a pointer (as in C) to a buffer within another buffer. It accepts a handle to a buffer (handle2$ in the synopsis) and stores it as a pointer at the given offset within the buffer given first (handle1$). The arguments are:

  • A handle to a buffer, that might have been just allocated or been returned from a foreign function call.

  • An offset, specifying the first byte where the pointer to the given buffer will be stored.

  • A handle to a buffer whose address (pointer) will be stored within the first buffer.


Name

foreign_buffer_size() — return the size of the foreign buffer

Synopsis

size = foreign_buffer_size(handle$)

Description

Return the size of the given buffer; if your handle just encapsulates a null-pointer, this will return 0; if the size is not known (standard for buffers returned from a foreign function call), the size will be -1.


Name

foreign_function_call() — call a function (returning a number) from a non-yabasic library or dll

Synopsis

print foreign_function_call("libtimestwo","int","timestwo","int",3)

Description

foreign_function_call calls a function from an external library.

In general, this feature is mostly useful, if you have such a library written or aquired. If you have an external command, that can be called interactively (i.e. from the commandline), you might try the system-function.

Please see the overview-section on foreign functions for overview, background and more examples. For details on functionality and arguments see below.

The example uses the foreign_function_call to invoke the cos-function from the standard C-library (libm.so.6 under Unix or msvcrt.dll under Windows).

Example

if peek$("os") = "unix" then
  lib$ = "libm.so.6"
else
  lib$ = "msvcrt.dll"
fi
print foreign_function_call(lib$,"double","cos","double",2)	      
          

The foreign_function_call-function accepts a variable number of arguments; 3 at minimum, 5 in the example above:

  • A string, containing the name of the library, e.g. "libm.so.6".

  • A string describing the type, that the function (specified with the next argument) returns (in the example: "double"). See below for a list of all such types.

  • The name of the function, that should be called (in the example above: "cos")

If the external function does not require arguments itself, the three arguments above are everything needed for foreign_function_call. However (as for cos), if the external function itself requires arguments, than for each of its arguments, two more arguments are needed foreign_function_call:

  • A string describing the type of the parameter to the external function (in the example: "double"). See the overview-section on foreign functions for a list of all such types.

  • A value, that can be converted to the specified type (in the example: 2).

With all these arguments specified, yabasic will call the foreign function (in the example: cos) and return its result; this process can be influenced by specifying options (see below).

Options

Options can be appended in any number after the string "options", e.g. like:

	      foreign_function_call(lib$,"double","cos","double",2,"options","error")
	    

Each option can be preceded with the string no_ to invert its meaning. As given below (i.e. with or without no_) the values represent the respective default.

error

In case of errors (e.g. if a library cannot be found), should the function report them actively (which terminates your yabasic-program) ? Or should the error silently stored away for later retrieval by peek("last_foreign_function_call_okay") and peek$("last_foreign_function_call_error_text") ?

no_copy_string_result

If the foreign function returns a string-value (like strstr), it should be invoked using foreign_function_call$, which returns a string. Now, depending on the foreign function invoked, it might be necessary to make a copy of its result before returning it to yabasic. In the case of strstr this is needed, because it returns just a pointer to part of its input string which will yabasic happily free later on, probably leading to a segfault after.

no_unload_library

Normally, after making a call to a foreign function, the named library is kept in memory for further use (see background). However, sometimes you might want to dismiss the library right after the call; then you may specify this option.


Name

foreign_function_call$() — call a function (returning a string or a buffer) from a non-yabasic library or dll

Synopsis

a$=foreign_function_call$("libupper","string","toupper","string","hello world")	    

Description

This function calls a function from an external library, just like foreign_function_call (which see for most of the description). The only difference is that foreign_function_call$ should be used when the foreign function returns a string or a structure (which itself is contained in a buffer, which is represented by a handle, which is a string).

The arguments are just the same as in foreign_function_call, only the second argument ("string" in the example above) can only be "string" or "buffer" in accord to the nature of foreign_function_call$, which itself must return a string.

Among the options described at foreign_function_call, the option "copy_string_result" can really only be applied here.


Name

foreign_function_size() — return the size of one of the types available for foreign function calls

Synopsis

offset=foreign_function_size("short")

Description

The function returns the size of any of the types available for calls to foreign functions (see the overview section for a complete list). This is useful when calculating offsets needed for foreign_buffer_set or foreign_buffer_get.


Name

frnbf_ and frnfn_ — Abbreviations for foreign_buffer_ and foreign_function_

Synopsis

print frnfn_size("short")

Description

The abbreviations frnbf_ and frnfn_ are just short for foreign_buffer_ and foreign_function_; you might prefer one over the other; in any case a good editor should make it easy to replace the short form with the long one.


Name

frac() — return the fractional part of its numeric argument

Synopsis

x=frac(y)

Description

The frac-function takes its argument, removes all the digits to the left of the comma and just returns the digits right of the comma, i.e. the fractional part.

Refer to the example to learn how to rewrite frac by employing the int-function (which is not suggested anyway).

Example

for a=1 to 10
  print frac(sqr(a))
  print sqr(a)-int(sqr(a))
next a
          

The example prints the fractional part of the square root of the numbers between 1 and 10. Each result is computed (and printed) twice: Once by employing the frac-function and once by employing the int-function.

See also

int, floor, ceil, round

G

getbit$() — return a string representing the bit pattern of a rectangle within the graphic window
getscreen$() — returns a string representing a rectangular section of the text terminal
glob() — check if a string matches a simple pattern
gosub — continue execution at another point within your program (and return later)
goto — continue execution at another point within your program (and never come back)

Name

getbit$() — return a string representing the bit pattern of a rectangle within the graphic window

Synopsis

a$=getbit$(10,10,20,20)
a$=getbit$(10,10 to 20,20)

Description

The function getbit returns a string, which contains the encoded bit-pattern of a rectangle within graphic window; the four arguments specify two opposite corners of the rectangle. The string returned might later be fed to the putbit-command.

The getbit$-function might be used for simple animations (as in the example below).

Example

open window 40,40
fill circle 20,20,18
circle$=getbit$(0,0,40,40)
close window

open window 200,200
for x=1 to 200
  putbit circle$,x,80
next x
          

This example features a circle moving from left to right over the window.

See also

putbit


Name

getscreen$() — returns a string representing a rectangular section of the text terminal

Synopsis

a$=getscreen$(2,2,20,20)

Description

The getscreen$ function returns a string representing the area of the screen as specified by its four arguments (which specify two opposite corners). I.e. everything you have printed within this rectangle will be encoded in the string returned (including any colour-information).

Like most other commands dealing with advanced text output, getscreen$ requires, that you have called clear screen before.

Example

clear screen

for a=1 to 1000:
	print color("red") "1";
	print color("green") "2";
	print color("blue") "3";
next a  
screen$=getscreen$(10,10,40,10)
print at(10,10) " Please Press 'y' or 'n' ! "
a$=inkey$
putscreen screen$,10,10
          

This program fills the screen with colored digits and afterwards asks the user for a choice ( Please press 'y' or 'n' ! ). Afterwards the area of the screen, which has been overwritten by the question will be restored with its previous contents, whhch had been saved via getscreen$.

See also

putscreen$


Name

glob() — check if a string matches a simple pattern

Synopsis

if (glob(string$,pattern$)) …

Description

The glob-function takes two arguments, a string and a (glob-) pattern, and checks if the string matches the pattern. However glob does not employ the powerful rules of regular expressions; rather it has only two special characters: * (which matches any number (even zero) of characters) and ? (which matches exactly a single character).

Example

for a=1 to 10
  read string$,pattern$
  if (glob(string$,pattern$)) then
    print string$," matches ",pattern$
  else
    print string$," does not match ",pattern$
  endif
next a

data "abc","a*"
data "abc","a?"
data "abc","a??"
data "abc","*b*"
data "abc","*"
data "abc","???"
data "abc","?"
data "abc","*c"
data "abc","A*"
data "abc","????"
          

This program checks the string abc against various patterns and prints the result. The output is:

abc matches a*
abc does not match a?
abc matches a??
abc matches *b*
abc matches *
abc matches ???
abc does not match ?
abc matches *c
abc does not match A*
abc does not match ????

See also

There are no related commands.


Name

gosub — continue execution at another point within your program (and return later)

Synopsis

gosub foo

…

label foo
…
return

Description

gosub remembers the current position within your program and then passes the flow of execution to another point (which is normally marked with a label). Later, when a return-statement is encountered, the execution is resumed at the previous location.

gosub is the traditional command for calling code, which needs to be executed from various places within your program. However, with subroutines yabasic offers a much more flexible way to achieve this (and more). Therefore gosub must to be considered obsolete.

Example

print "Do you want to exit ? "
gosub ask
if (r$="y") exit

label ask
input "Please answer yes or no, by typing 'y' or 'n': ",r$
return
          

Name

goto — continue execution at another point within your program (and never come back)

Synopsis

goto foo

…

label foo

Description

The goto-statement passes the flow of execution to another point within your program (which is normally marked with a label).

goto is normally considered obsolete and harmful, however in yabasic it may be put to the good use of leaving loops (e.g. while or for) prematurely. Note however, that subroutines may not be left with the goto-statement.

Example

print "Please press any key to continue."
print "(program will continue by itself within 10 seconds)"
for a=1 to 10
  if (inkey$(1)<>"") then goto done
next a
label done
print "Hello World !"
          

Here the goto-statement is used to leave the for-loop prematurely.

See also

gosub, on goto

H

hex$() — convert a number into hexadecimal

Name

hex$() — convert a number into hexadecimal

Synopsis

print hex$(foo)

Description

The hex$-function converts a number into a string with its hexadecimal representation. hex$ is the inverse of the dec-function.

Example

open 1,"foo"
while !eof(1)
  print right$("0"+hex$(peek(1)),2)," ";
  i=i+1
  if (mod(i,10)=0) print
end while
print
          

This program reads the file foo and prints its output as a hex-dump using the hex-function.

I

if — evaluate a condition and execute statements or not, depending on the result
import — import a library
inkey$ — wait, until a key is pressed
input — read input from the user (or from a file) and assign it to a variable
instr() — searches its second argument within the first; returns its position if found
int() — return the integer part of its single numeric argument

Name

if — evaluate a condition and execute statements or not, depending on the result

Synopsis

if (…) then
  …
endif

if (…) …

if (…) then
  …
else
  …
endif

if (…) then
  …
elsif (…)
  …
elsif (…) then
  …
else
  …
endif

Description

The if-statement is used to evaluate a conditions and take actions accordingly. (As an aside, please note that there is no real difference between conditions and expressions.)

There are two major forms of the if-statement:

  • The one-line-form without the keyword then:

    if (…) …

    This form evaluates the condition and if the result is true executes all commands (separated by colons) upt to the end of the line. There is neither an endif keyword nor an else-branch.

  • The multi-line-form with the keyword then:

    if (…) then … elsif (…) … else … endif

    (where elsif and else are optional, whereas endif is not.

    According to the requirements of your program, you may specify:

    • elsif(…), which specifies a condition, that will be evaluated only if the condition(s) within if or any preceding elsif did not match.

    • else, which introduces a sequence of commands, that will be executed, if none of the conditions above did match.

    • endif is required and ends the if-statement.

Example

input "Please enter a number between 1 and 4: " a
if (a<=1 or a>=4) error "Wrong, wrong !"
if (a=1) then
  print "one"
elsif (a=2)
  print "two"
elsif (a=3)
  print "three"
else
  print "four"
endif
          

The input-number between 1 and 4 is simply echoed as text (one, two, …). The example demonstrates both forms (short and long) of the if-statement (Note however, that the same thing can be done, probably somewhat more elegant, with the switch-statement).


Name

import — import a library

Synopsis

import foo

Description

The import-statement imports a library. It expects a single argument, which must be the name of a library (without the trailing .yab). This library will then be read and parsed and its subroutines (and variables) will be made available within the importing program. Most of the time this will be the main program, but libraries my also import and use other libraries.

Libraries will first be searched in three locations in order:

  • The current directory, i.e. the directory from which you have invoked yabasic)

  • The directory, where your main program lives. This can be different from the first directory, if you specify a path for your main program, e.g. like yabasic foo/bar.yab.

  • Finally, libraries are searched within a special directory, whose exact location depends on your system or options when invoking yabasic. Typical values would be /usr/lib under Unix or C:\yabasic\lib under Windows. Invoking yabasic --help will show the correct directory. The location of this directory may be changed with the option --librarypath (see options).

Example

Lets say you have a yabasic-program foo.yab, which imports a library lib.yab. foo.yab; this would read:

import lib

rem  This works
lib.x(0)

rem  This works too
x(1)

rem  And this
lib.y(2)

rem  But this not !
y(3)
          

Now the library lib.yab reads:

rem  Make the subroutine x easily available outside this library
export sub x(a)
  print a
  return
end sub

rem  sub y must be referenced by its full name
rem  outside this library
sub y(a)
  print a
  return
end sub

This program produces an error:

0
1
2
---Error in foo.yab, line 13: can't find subroutine 'y'
---Dump: sub y() called in foo.yab,13
---Error: Program stopped due to an error

As you may see from the error message, yabasic is unable to find the subroutine y without specifying the name of the library (i.e. lib.y). The reason for this is, that y, other than x, is not exported from the library lib.yab (using the export-statement).

See also

export, sub


Name

inkey$ — wait, until a key is pressed

Synopsis

clear screen
foo$=inkey$
inkey$
foo$=inkey$(bar)
inkey$(bar)

Description

The inkeys$-function waits, until the user presses a key on the keyboard or a button of his mouse, and returns this very key. An optional argument specifies the number of seconds to wait; if omitted, inkey$ will wait indefinitely.

inkey$ may only be used, if clear screen has been called at least once.

For normal keys, yabasic simply returns the key, e.g. a, 1 or !. For function keys you will get f1, f2 and so on. Other special keys will return these strings respectively: enter, backspace, del, esc, scrnup (for screen up), scrndown and tab. Modifier keys (e.g. ctrl, alt or shift) by themselves can not be detected (e.g. if you simultaneously press shift and 'a', inkey$ will return the letter 'A' instead of 'a' of course).

If a graphical window has been opened (via open window) any mouseclick within this window will be returned by inkey$ too. The string returned (e.g. MB1d+0:0028,0061, MB2u+0:0028,0061 or MB1d+1:0028,0061) is constructed as follows:

  • Every string associated with a mouseclick will start with the fixed string MB

  • The next digit (1, 2 or 3) specifies the mousebutton pressed.

  • A single letter, d or u, specifies, if the mousebutton has been pressed or released: d stands for down, i.e. the mousebutton has been pressed; u means up, i.e. the mousebutton has been released.

  • The plus-sign ('+'), which follows is always fixed.

  • The next digit (in the range 0 to 7) encodes the modifier keys pressed, where 1 stands for shift, 2 stands for alt and 4 stands for ctrl.

  • The next four digits (e.g. 0028) contain the x-position, where the mousebutton has been pressed.

  • The comma to follow is always fixed.

  • The last four digits (e.g. 0061) contain the y-position, where the mousebutton has been pressed.

All those fields are of fixed length, so you may use functions like mid$ to extract certain fields. However, note that with mousex, mousey, mouseb and mousemod there are specialized functions to return detailed information about the mouseclick. Finally it should be noted, that inkey$ will only register mouseclicks within the graphic-window; mouseclicks in the text-window cannot be detected.

inkey$ accepts an optional argument, specifying a timeout in seconds; if no key has been pressed within this span of time, an empty string is returned. If the timeout-argument is omitted, inkey$ will wait for ever.

Example

clear screen
open window 100,100
print "Press any key or press 'q' to stop."
repeat
  a$=inkey$
  print a$
until a$="q"
          

This program simply returns the key pressed. You may use it, to learn, which strings are returned for the special keys on your keyboard (e.g. function-keys).


Name

input — read input from the user (or from a file) and assign it to a variable

Synopsis

input a
input a,b,c
input a$
input "Hello" a
input #1 a$

Description

input reads the new contents of one or many (numeric- or string-) variables, either from the keyboard (i.e. from you) or from a file. An optional first string-argument specifies a prompt, which will be issued before reading any contents.

If you want to read from an open file, you need to specify a hash ('#'), followed by the number, under which the file has been opened.

Note, that the input is split at spaces, i.e. if you enter a whole line consisting of many space-separated word, the first input-statement will only return the first word; the other words will only be returned on subsequent calls to input; the same applies, if a single input reads multiple variables: The first variable gets only the first word, the second one the second word, and so on. If you don't like this behaviour, you may use line input, which returns a whole line (including embedded spaces) at once.

Example

input "Please enter the name of a file to read: " a$
open 1,a$
while !eof(1)
  input #1 b$
  print b$
wend
          

If this program is stored within a file test.yab and you enter this name when prompted for a file to read, you will see this output:

Please enter the name of a file to read: t.yab
input
"Please
enter
the
name
of
a
file
to
read:
"
a$
open
1,a$
while
!eof(1)
input
#1
b$
print
b$
wend

See also

line input


Name

instr() — searches its second argument within the first; returns its position if found

Synopsis

print instr(a$,b$)
if (instr(a$,b$)) …
pos=instr(a$,b$,x)

Description

The instr-functions requires two string arguments and searches the second argument within the first. If the second argument can be found within the first, the position is returned (counting from one). If it can not be found, the instr-function returns 0; this makes this function usable within the condition of an if-statement (see the example below).

If you supply a third, numeric argument to the instr-function, it will be used as a starting point for the search. Therefore instr("abcdeabcdeabcde","e",8) will return 10, because the search for an "e" starts at position 8 and finds the "e" at position 10 (and not the one at position 5).

Example

input "Please enter a text containing the string 'cat': " a$
if (instr(a$,"cat")) then
  print "Well done !"
else
  print "No cat in your input ..."
endif
          

See also

rinstr


Name

int() — return the integer part of its single numeric argument

Synopsis

print int(a)

Description

The int-function returns only the digits before the comma; int(2.5) returns 2 and int(-2.3) returns -2.

Example

input "Please enter a whole number between 1 and 10: " a
if (a=int(a) and a>=1 and a<=10) then
  print "Thanx !"
else
  print "Never mind ..."
endif
          

See also

frac, floor, ceil, round

L

label — mark a specific location within your program for goto, gosub or restore
left$() — return (or change) left end of a string
len() — return the length of a string
line — draw a line
line input — read in a whole line of text and assign it to a variable
local — mark a variable as local to a subroutine
log() — compute the natural logarithm
loop — marks the end of an infinite loop
lower$() — convert a string to lower case
ltrim$() — trim spaces at the left end of a string

Name

label — mark a specific location within your program for goto, gosub or restore

Synopsis

label foo

…

goto foo

Description

The label-command can be used to give a name to a specific location within your program. Such a position might be referred from one of three commands: goto, gosub and restore.

You may use labels safely within libraries, because a label (e.g. foo) does not collide with a label with the same name within the main program or within another library; yabasic will not mix them up.

As an aside, please note, that line numbers are a special (however deprecated) case of labels; see the second example below.

Example

for a=1 to 100
  if (ran(10)>5) goto done
next a
label done

10 for a=1 to 100
20   if (ran(10)>5) goto 40
30 next a
40
          

Within this example, the for-loop will probably be left prematurely with a goto-statement. This task is done twice: First with labels and then again with line numbers.

See also

gosub, goto.


Name

left$() — return (or change) left end of a string

Synopsis

print left$(a$,2)
left$(b$,3)="foobar"

Description

The left$-function accepts two arguments (a string and a number) and returns the part from the left end of the string, whose length is specified by its second argument. Loosely spoken, it simply returns the requested number of chars from the left end of the given string.

Note, that the left$-function can be assigned to, i.e. it may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the left$-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.

Example

input "Please answer yes or no: " a$
l=len(a$):a$=lower$(a$):print "Your answer is ";
if (left$("yes",l)=a$ and l>=1) then
  print "yes"
elsif (left$("no",l)=a$ and l>=1) then
  print "no"
else
  print "?"
endif
          

This example asks a simple yes/no question and goes some way to accept even incomplete input, while still being able to reject invalid input.

This second example demonstrates the capability to assign to the left$-function.

a$="Heiho World !"
print a$
left$(a$,5)="Hello"
print a$

See also

right$, mid$


Name

len() — return the length of a string

Synopsis

x=len(a$)

Description

The len-function returns the length of its single string argument.

Example

input "Please enter a password: " a$
if (len(a$)<6) error "Password too short !"
          

This example checks the length of the password, that the user has entered.

See also

left$, right$ and mid$,


Name

line — draw a line

Synopsis

open window 100,100
line 0,0,100,100
line 0,0 to 100,100
new curve
line 100,100
line to 100,100

open window 100,100
clear line 0,0,100,100
clear line 0,0 to 100,100
new curve
clear line 100,100
clear line to 100,100

Description

The line-command draws a line. Simple as this is, the line-command has a large variety of forms as they are listed in the synopsis above. Lets look at them a little closer:

  • A line has a starting and an end point; therefore the line-command (normally) needs four numbers as arguments, representing these two points. This is the first form appearing within the synopsis.

  • You may separate the two points with either ',' or to, which accounts for the second form of the line-command.

  • The line-command may be used to draw a connected sequence of lines with a sequence of commands like line x,y; Each command will draw a line from the point where the last line-command left off, to the point specified in the arguments. Note, that you need to use the command new curve before you may issue such a line-command. See the example below.

  • You may insert the word to for beauty: line to x,y, which does exactly the same as line x,y

  • Finally, you may choose not to draw, but to erase the lines; this can be done by prepending the phrase clear. This account for all the other forms of the line-command.

Example

open window 200,200
line 10,10 to 10,190
line 10,190 to 190,190
new curve
for a=0 to 360
  line to 10+a*180/360,100+60*sin(a*pi/180)
next a
          

This example draws a sine-curve (with an offset in x- and y-direction). Note, that the first line-command after new curve does not draw anything. Only the coordinates will be stored. The second iteration of the loop then uses these coordinates as a starting point for the first line.


Name

line input — read in a whole line of text and assign it to a variable

Synopsis

line input a
line input a$
line input "Hello" a
line input #1 a$

Description

In most respects line input is like the input-command: It reads the new contents of a variable, either from keyboard or from a file. However, line input always reads a complete line and assigns it to its variable. line input does not stop reading at spaces and is therefore the best way to read in a string which might contain whitespace. Note, that the final newline is stripped of.

Example

line input "Please enter your name (e.g. Frodo Beutelin): " a$
print "Hello ",a$
          

Note that the usage of line input is essential in this example; a simple input-statement would only return the string up to the first space, e.g. Frodo.

See also

input


Name

local — mark a variable as local to a subroutine

Synopsis

sub foo()

  local a,b,c$,d(10),e$(5,5)

  …

end sub 

Description

The local-command can (and should be) used to mark a variable (or array) as local to the containing subroutine. This means, that a local variable in your subroutine is totally different from a variable with the same name within your main program. Variables which are known everywhere within your program are called global in contrast.

Declaring variables within the subroutine as local helps to avoid hard to find bugs; therefore local variables should be used whenever possible.

Note, that the parameters of your subroutines are always local.

As you may see from the example, local arrays may be created without using the keyword dim (which is required only for global arrays).

Example

a=1
b=1
print a,b
foo()
print a,b

sub foo()
  local a
  a=2
  b=2
end sub
          

This example demonstrates the difference between local and global variables; it produces this output:

1 1
1 2

As you may see, the content of the global variable a is unchanged after the subroutine foo; this is because the assignment a=2 within the subroutine affects the local variable a only and not the global one. However, the variable b is never declared local and therefore the subroutine changes the global variable, which is reflected in the output of the second print-statement.

See also

sub, static, dim


Name

log() — compute the natural logarithm

Synopsis

a=log(x)
a=log(x,base)

Description

The log-function computes the logarithm of its first argument. The optional second argument gives the base for the logarithm; if this second argument is omitted, the euler-constant 2.71828… will be taken as the base.

Example

open window 200,200
for x=10 to 190 step 10:for y=10 to 190 step 10
  r=3*log(1+x,1+y)
  if (r>10) r=10
  if (r<1) r=1
  fill circle x,y,r
next y:next x
          

This draws another nice plot.

See also

exp


Name

loop — marks the end of an infinite loop

Synopsis

do
  …
loop

Description

The loop-command marks the ends of a loop (which is started by do), wherein all statements within the loop are repeated forever. In this respect the do loop-loop is infinite, however, you may leave it anytime via break or goto.

Example

print "Hello, I will throw dice, until I get a 2 ..."
do
  r=int(ran(6))+1
  print r
  if (r=2) break
loop
          

See also

do, for, repeat, while, break


Name

lower$() — convert a string to lower case

Synopsis

l$=lower$(a$)

Description

The lower$-function accepts a single string-argument and converts it to all lower case.

Example

input "Please enter a password: " a$
if (a$=lower$(a$)) error "Your password is NOT mixed case !"
          

This example prompts for a password and checks, if it is really lower case.

See also

upper$


Name

ltrim$() — trim spaces at the left end of a string

Synopsis

a$=ltrim$(b$)

Description

The ltrim$-function removes all whitespace from the left end of a string and returns the result.

Example

input "Please answer 'yes' or 'no' : " a$
a$=lower$(ltrim$(rtrim$(a$)))
if (len(a$)>0 and a$=left$("yes",len(a$))) then
  print "Yes ..."
else
  print "No ..."
endif
          

This example prompts for an answer and removes any spaces, which might precede the input; therefore it is even prepared for the (albeit somewhat pathological case, that the user first hits space before entering his answer.

See also

rtrim$, trim$

M

max() — return the larger of its two arguments
mid$() — return (or change) characters from within a string
min() — return the smaller of its two arguments
mod — compute the remainder of a division
mouseb — extract the state of the mousebuttons from a string returned by inkey$
mousemod — return the state of the modifier keys during a mouseclick
mousex — return the x-position of a mouseclick
mousey — return the y-position of a mouseclick

Name

max() — return the larger of its two arguments

Synopsis

print max(a,b)

Description

Return the maximum of its two arguments.

Example

dim m(10)
for a=1 to 1000
  m=0
  For b=1 to 10
    m=max(m,ran(10))
  next b
  m(m)=m(m)+1
next a

for a=1 to 9
  print a,": ",m(a)
next a
          

Within the inner for-loop (the one with the loop-variable b), the example computes the maximum of 10 random numbers. The outer loop (with the loop variable a) now repeats this process 1000 times and counts, how often each maximum appears. The last loop finally reports the result.

Now, the interesting question would be, which will be approached, when we increase the number of iterations from thousand to infinity. Well, maybe someone could just tell me :-)

See also

min


Name

mid$() — return (or change) characters from within a string

Synopsis

print mid$(a$,2,1)
print mid$(a$,2)
mid$(a$,5,3)="foo"
mid$(a$,5)="foo"

Description

The mid$-function requires three arguments: a string and two numbers, where the first number specifies a position within the string and the second one gives the number of characters to be returned; if you omit the second argument, the mid$-function returns all characters up to the end of the string.

Note, that you may assign to the mid$-function, i.e. mid$ may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the mid$-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.

Example

input "Please enter a string: " a$
for a=1 to len(a$)
  if (instr("aeiou",lower$(mid$(a$,a,1)))) mid$(a$,a,1)="e"
next a
print "When you turn everything to lower case and"
print "replace every vowel with 'e', your input reads:"
print
print a$
          

This example transforms the input string a bit, using the mid$-function to retrieve a character from within the string as well as to change it.

See also

left$ and right$.


Name

min() — return the smaller of its two arguments

Synopsis

print min(a,b)

Description

Return the minimum of its two argument.

Example

dim m(10)
for a=1 to 1000
  m=min(ran(10),ran(10))
  m(m)=m(m)+1
next a

for a=1 to 9
  print a,": ",m(a)
next a
          

For each iteration of the loop, the lower of two random number is recorded. The result is printed at the end.

See also

max


Name

mod — compute the remainder of a division

Synopsis

print mod(a,b)

Description

The mod-function divides its two arguments and computes the remainder. Note, that a/b-int(a/b) and mod(a,b) are always equal.

Example

clear screen
print at(10,10) "Please wait ";
p$="-\|/"
for a=1 to 100
  rem  ... do something lengthy here, or simply sleep :-)
  pause(1)
  print at(22,10) mid$(p$,1+mod(a,4))
next a
          

This example executes some time consuming action within a loop (in fact, it simply sleeps) and gives the user some indication of progress by displaying a rotating bar (that's where the mod-function comes into play).

See also

int, frac, round


Name

mouseb — extract the state of the mousebuttons from a string returned by inkey$

Synopsis

inkey$
print mouseb()
print mouseb
a$=inkey$
print mouseb(a$)

Description

The mouseb-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function. If a mousebutton has been pressed, the mouseb-function returns the number (1,2 or 3) of the mousebutton, when it is pressed and returns its negative (-1,-2 or -3), when it is released.

The mouseb-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mouseb is called without any arguments, it returns the values from the last call to inkey$, which are stored implicitly and internally by yabasic.

Note

Note however, that the value returned by the mouseb-function does not reflect the current state of the mousebuttons. It rather extracts the information from the string passed as an argument (or from the last call to the inkey$-function, if no argument is passed). So the value returned by mouseb reflects the state of the mousebuttons at the time the inkey$-function has been called; as opposed to the time the mouseb-function is called.

Example

open window 200,200
clear screen
print "Please draw lines; press (and keep it pressed)" 
print "the left mousebutton for the starting point,"
print "release it for the end-point."
do
  if (mouseb(release$)=1) press$=release$
  release$=inkey$
  if (mouseb(release$)=-1) then
    line mousex(press$),mousey(press$) to mousex(release$),mousey(release$)
  endif
loop
          

This is a maybe the most simplistic line-drawing program possible, catching presses as well as releases of the first mousebutton.


Name

mousemod — return the state of the modifier keys during a mouseclick

Synopsis

inkey$
print mousemod()
print mousemod
a$=inkey$
print mousemod(a$)

Description

The mousemod-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function if a mousebutton has been pressed. It returns the state of the keyboard modifiers (shift, ctrl or alt): If the shift-key is pressed, mousemod returns 1, for the alt-key 2 and for the ctrl-key 4. If more than one key is pressed, the sum of these values is returned, e.g. mousemod returns 5, if shift and ctrl are pressed simultaneously.

The mousemod-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mousemod is called without any arguments, it returns the values from the last call to inkey$ (which are stored implicitly and internally by yabasic).

Note

Please see also the Note within the mouseb-function.

Example

open window 200,200
clear screen
do
  a$=inkey$
  if (left$(a$,2)="MB") then
    x=mousex(a$)
    y=mousey(a$)
    if (mousemod(a$)=0) then
      circle x,y,20
    else
      fill circle x,y,20
    endif
  endif
loop
          

This program draws a circle, whenever a mousebutton is pressed; the circles are filled, when any modifier is pressed, and empty if not.

See also

inkey$, mousex, mousey and mouseb


Name

mousex — return the x-position of a mouseclick

Synopsis

inkey$
print mousex()
print mousex
a$=inkey$
print mousex(a$)

Description

The mousex-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function; It returns the x-position of the mouse as encoded within its argument.

The mousex-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mousex is called without any arguments, it returns the values from the last call to inkey$ (which are stored implicitly and internally by yabasic).

Note

Please see also the Note within the mouseb-function.

Example

open window 200,200
clear screen
do
  a$=inkey$
  if (left$(a$,2)="MB") then
    line mousex,0 to mousex,200
  endif
loop
          

This example draws vertical lines at the position, where the mousebutton has been pressed.


Name

mousey — return the y-position of a mouseclick

Synopsis

inkey$
print mousey()
print mousey
a$=inkey$
print mousey(a$)

Description

The mousey-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function. mousey returns the y-position of the mouse as encoded within its argument.

The mousey-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mousey is called without any arguments, it returns the values from the last call to inkey$ (which are stored implicitly and internally by yabasic).

Note

Please see also the Note within the mouseb-function.

Example

open window 200,200
clear screen
do
  a$=inkey$
  if (left$(a$,2)="MB") then
    line 0,mousey to 200,mousey
  endif
loop
          

This example draws horizontal lines at the position, where the mousebutton has been pressed.

N

new curve — start a new curve, that will be drawn with the line-command
next — mark the end of a for loop
not — negate a logical expression; can be written as !
numparams — return the number of parameters, that have been passed to a subroutine

Name

new curve — start a new curve, that will be drawn with the line-command

Synopsis

new curve
line to x,y

Description

The new curve-function starts a new sequence of lines, that will be drawn by repeated line to-commands.

Example

open window 200,200
ellipse(100,50,30,60)
ellipse(150,100,60,30)
sub ellipse(x,y,xr,yr)
  new curve
  for a=0 to 2*pi step 0.2
    line to x+xr*cos(a),y+yr*sin(a)
  next a
  close curve
end sub
  
          

This example defines a subroutine ellipse that draws an ellipse. Within this subroutine, the ellipse is drawn as a sequence of lines started with the new curve command and closed with close curve.

See also

line, close curve


Name

next — mark the end of a for loop

Synopsis

for a=1 to 10
next a

Description

The next-keyword marks the end of a for-loop. All statements up to the next-keyword will be repeated as specified with the for-clause. Note, that the name of the variable is optional; so instead of next a you may write next.

Example

for a=1 to 300000
  for b=1 to 21+20*sin(pi*a/20)
    print "*";
  next b
  print
  sleep 0.1
next a
          

This example simply plots a sine-curve until you fall asleep.

See also

for


Name

not — negate a logical expression; can be written as !

Synopsis

if not a<b then …
bad=!okay

Description

The keyword not (or ! for short) is mostly used within conditions (e.g. within if- or while-statements). There it is employed to negate the condition or expression (i.e. turn TRUE into FALSE and vice versa)

However not can be used within arithmetic calculations too., simply because there is no difference between arithmetic and logical expressions.

Example

input "Please enter three ascending numbers: " a,b,c
if (not (a<b and b<c)) error " the numbers you have entered are not ascending ..."
          

See also

and,or


Name

numparams — return the number of parameters, that have been passed to a subroutine

Synopsis

sub foo(a,b,c)
  if (numparams=1) …
  …
end sub

Description

Within a subroutine the local variable numparam or numparams contains the number of parameters, that have been passed to the subroutine. This information can be useful, because the subroutine may have been called with fewer parameters than actually declared. The number of values that actually have been passed while calling the subroutine, can be found in numparams.

Note, that arguments which are used in the definition of a subroutine but are left out during a call to it (thereby reducing the value of numparams) receive a value of 0 or "" (empty string) respectively.

Example

a$="123456789"
print part$(a$,4)
print part$(a$,3,7)

sub part$(a$,f,t)
  if (numparams=2) then
    return mid$(a$,f)
  else 
    return mid$(a$,f,t-f+1)
  end if
end sub
          

When you run this example, it will print 456789 and 34567. Take a look at the subroutine part$, which returns part of the string which has been passed as an argument. If (besides the string) two numbers are passed, they define the starting and end position of the substring, that will be returned. However, if only one number is passed, the rest of the string, starting from this position will be returned. Each of these cases is recognized with the help of the numparams variable.

See also

sub

O

on gosub — jump to one of multiple gosub-targets
on goto — jump to one of many goto-targets
on interrupt — change reaction on keyboard interrupts
open — open a file
open printer — open printer for printing graphics
open window — open a graphic window
logical or — logical or, used in conditions
or() — arithmetic or, used for bit-operations

Name

on goto — jump to one of multiple gosub-targets

Synopsis

on a gosub foo,bar,baz
  …
label foo
  …
return

label bar
  …
return

label baz
  …
return

Description

The on gosub statement uses its numeric argument (the one between on and gosub) to select an element from the list of labels, which follows after the gosub-keyword: If the number is 1, the program does a gosub to the first label; if the number is 2, to the second and, so on. if the number is zero or less, the program continues at the position of the first label; if the number is larger than the total count of labels, the execution continues at the position of the last label; i.e. the first and last label in the list constitute some kind of fallback-slot.

Note, that the on gosub-command can no longer be considered state of the art; people (not me !) may even start to mock you, if you use it.

Example

do
  print "Please enter a number between 1 and 3: "
  print
  input "Your choice " a
  on a gosub bad,one,two,three,bad
loop

label bad
  print "No. Please between 1 and 3"
return

label one
  print "one"
return

label two
  print "two"
return

label three
  print "three"
return
          

Note, how invalid input (a number less than 1, or larger than 3) is automatically detected.


Name

on goto — jump to one of many goto-targets

Synopsis

on a goto foo,bar,baz
  …
label foo
  …
label bar
  …
label baz
  …

Description

The on goto statement uses its numeric argument (the one between on and goto to select an element from the list of labels, which follows after the goto-keyword: If the number is 1, the execution continues at the first label; if the number is 2, at the second, and so on. if the number is zero or less, the program continues at the position of the first label; if the number is larger than the total count of labels, the execution continues at the position of the last label; i.e. the first and last label in the list constitute some kind of fallback-slot.

Note, that (unlike the goto-command) the on goto-command can no longer be considered state of the art; people may (not me !) even start to mock you, if you use it.

Example

label over
print "Please Select one of these choices: "
print
print "  1 -- show time"
print "  2 -- show date"
print "  3 -- exit"
print
input "Your choice " a
on a goto over,show_time,show_date,terminate,over

label show_time
  print time$()
goto over

label show_date
  print date$()
goto over

label terminate
exit
          

Note, how invalid input (a number less than 1, or larger than 3) is automatically detected; in such a case the question is simply issued again.


Name

on interrupt — change reaction on keyboard interrupts

Synopsis

on interrupt break
…
on interrupt continue

Description

With the on interrupt-command you may change the way, how yabasic reacts on a keyboard interrupt; it comes in two variants: on interrupt break and on interrupt continue. A keyboard interrupt is produced, if you press ctrl-C on your keyboard; normally (and certainly after you have called on interrupt break), yabasic will terminate with an error message. However after the command on interrupt continue yabasic ignores any keyboard interrupt. This may be useful, if you do not want your program being interruptible during certain critical operations (e.g. updating of files).

Example

print "Please stand by while writing a file with random data ..."
on interrupt continue
open "random.data" for writing as #1
for a=1 to 100
  print #1 ran(100)
  print a," percent done."
  sleep 1
next a
close #1
on interrupt continue
          

This program writes a file with 100 random numbers. The on interrupt continue command insures, that the program will not be terminated on a keyboard interrupt and the file will be written entirely in any case. The sleep-command just stretches the process artificially to give you a chance to try a ctrl-C.

See also

There is no related command.


Name

open — open a file

Synopsis

open a,"file","r"
open #a,"file","w"
open #a,printer
open "file" for reading as a
open "file" for writing as #a
a=open("file")
a=open("file","r")
if (open(a,"file")) …
if (open(a,"file","w")) …

Description

The open-command opens a file for reading or writing or a printer for printing text. open comes in a wide variety of ways; it requires these arguments:

filenumber

In the synopsis this is a or #a. In yabasic each file is associated with a number between 1 and a maximum value, which depends on the operating system. For historical reasons the filenumber can be preceded by a hash ('#'). Note, that specifying a filenumber is optional; if it is omitted, the open-function will return a filenumber, which should then be stored in a variable for later reference. This filenumber can be a simple number or an arbitrary complex arithmetic expression, in which case braces might be necessary to save yabasic from getting confused.

filename

In the synopsis above this is "file". This string specifies the name of the file to open (note the important caveat on specifying these filenames).

accessmode

In the synopsis this is "r", "w", for reading or for writing. This string or clause specifies the mode in which the file is opened; it may be one of:

"r"

Open the file for reading (may also be written as for reading). If the file does not exist, the command will fail. This mode is the default, i.e. if no mode is specified with the open-command, the file will be opened with this mode.

"w"

Open the file for writing (may also be written as for writing). If the file does not exist, it will be created.

"a"

Open the file for appending, i.e. what you write to the file will be appended after its initial contents. If the file does not exist, it will be created.

"b"

This letter may not appear alone, but may be combined with the other letters (e.g. "rb") to open a file in binary mode (as opposed to text mode).

As you may see from the synopsis, the open-command may either be called as a command (without braces) or as a function (with braces). If called as a function, it will return the filenumber or zero if the operation fails. Therefore the open-function may be used within the condition of an if-statement.

If the open-command fails, you may use peek("error") to retrieve the exact nature of the error.

Furthermore note, that there is another, somewhat separate usage of the open-command; if you specify the bareword printer instead of a filename, the command opens a printer for printing text. Every text (and only text) you print to this file will appear on your printer. Note, that this is very different from printing graphics, as can be done with open printer.

Example

open "foo.bar" for writing as #1
print #1 "Hallo !"
close #1
if (not open(1,"foo.bar")) error "Could not open 'foo.bar' for reading"
while not eof(1)
  line input #1 a$
  print a$
wend
          

This example simply opens the file foo.bar, writes a single line, reopens it and reads its contents again.


Name

open printer — open printer for printing graphics

Synopsis

open printer
open printer "file"

Description

The open printer-command opens a printer for printing graphics. The command requires, that a graphic window has been opened before. Everything that is drawn into this window will then be sent to the printer too.

A new piece of paper may be started with the clear window-command; the final (or only) page will appear after the close printer-command.

Note, that you may specify a filename with open printer; in that case the printout will be sent to a filename instead to a printer. Your program or the user will be responsible for sending this file to the printer afterwards.

If you use yabasic under Unix, you will need a postscript printer (because yabasic produces postscript output). Alternatively you may use ghostscript to transform the postscript file into a form suitable for your printer; but that is beyond the responsibility of yabasic.

Example

open window 200,200
open printer
line 0,0 to 200,200
text 100,100,"Hallo"
close window
close printer
          

This example will open a window, draw a line and print some text within; everything will appear on your printer too.


Name

open window — open a graphic window

Synopsis

open window x,y
open window x,y,"font"

Description

The open window-command opens a window of the specified size. Only one window can be opened at any given moment of time.

An optional third argument specifies a font to be used for any text within the window. It can however be changed with any subsequent text-command.

Example

for a=200 to 400 step 10
  open window a,a
  for b=0 to a
    line 0,b to a,b
    line b,0 to b,a
  sleep 0.1
  close window
next a
          

Name

or — logical or, used in conditions

Synopsis

if a or b …
while a or b …

Description

Used in conditions (e.g within if or while) to join two expressions. Returns true, if either its left or its right or both arguments are true; returns false otherwise.

Example

input "Please enter a number"
if (a>9 or a<1) print "a is not between 1 and 9"
          

See also

and,bitnot


Name

or() — arithmetic or, used for bit-operations

Synopsis

x=or(a,b)

Description

Used to compute the bitwise or of both its argument. Both arguments are treated as binary numbers (i.e. a sequence of digits 0 and 1); a bit of the resulting value will then be 1, if any of its arguments has 1 at this position in their binary representation.

Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to or.

Example

print or(14,3)
          

This will print 15. This result is clear, if you note, that the binary representation of 14 and 3 are 1110 and 0011 respectively; this will yield 1111 in binary representation or 15 as decimal.

See also

and, eor and bitnot

P

pause — pause, sleep, wait for the specified number of seconds
peek — retrieve various internal information
peek$ — retrieve various internal string-information
pi — a constant with the value 3.14159
poke — change selected internals of yabasic
print — Write to terminal or file
print color — print with color
print colour — see print color
putbit — draw a rectangle of pixels encoded within a string into the graphics window
putscreen — draw a rectangle of characters into the text terminal

Name

pause — pause, sleep, wait for the specified number of seconds

Synopsis

pause 5

Description

The pause-command has many different names: You may write pause, sleep or wait interchangeably; whatever you write, yabasic will always do exactly the same.

The pause-command will simply wait for the specified number of seconds. This may be a fractional number, so you may well wait less than a second. However, if you try to pause for a smaller and smaller interval (e.g. 0.1 seconds, 0.01 seconds, 0.001 seconds and so on) you will find that at some point yabasic will not wait at all. The minimal interval that can be waited depends on the system (Unix, Windows) you are using.

The pause-command cannot be interrupted. However, sometimes you may want the wait to be interruptible by simply pressing a key on the keyboard. In such cases you should consider using the inkey$-function, with a number of seconds as an argument).

Example

deg=0
do
  maxx=44+40*sin(deg)
  for x=1 to maxx
    print "*";
  next x
  pause 0.1+(maxx*maxx/(4*84*84))
  print
  deg=deg+0.1
loop
          

This example draws a sine-curve; due to the pause-statement the speed of drawing varies in the same way as the speed of a ball might vary, if it would roll along this curve under the influence of gravity.

See also

sleep, wait


Name

peek — retrieve various internal information

Synopsis

print peek("foo")
a=peek(#1)

Description

The peek-function has many different and mostly unrelated uses. It is a kind of grab-bag for retrieving all kinds of numerical information, internal to yabasic. The meaning of the numbers returned be the peek-function depends on the string or number passed as an argument.

peek always returns a number, however the closely related peek$-function exists, which may be used to retrieve string information from among the internals of yabasic. Finally note, that some of the values which are retrieved with peek may even be changed, using the poke-function.

There are two variants of the peek-function: One expects an integer, positive number and is described within the first entry of the list below. The other variant expects one of a well defined set of strings as described in the second and all the following entries of the list below.

peek(a)

Read a single character from the file a (which must be open of course).

peek("argument")

Return the number of arguments, that have been passed to yabasic at invocation time. E.g. if yabasic has been called like this: yabasic foo.yab bar baz, then peek("argument") will return 2. This is because foo.yab is treated as the name of the program to run, whereas bar and baz are considered arguments to the program, which are passed on the command line. Note, that for windows-users, who tend to click on the icon (as opposed to starting yabasic on the command line), this peekwill mostly return 0.

The function peek("argument") can be written as peek("arguments") too.

You will want to check out the corresponding function peek$("argument") to actually retrieve the arguments. Note, that each call to peek$("argument") reduces the number returned by peek("argument").

peek("error")

Return a number specifying the nature of the last error in an open- or seek-statement. Normally an error within an open-statement immediately terminates your program with an appropriate error-message, so there is no chance and no need to learn more about the nature of the error. However, if you use open as a condition (e.g. if (open(#1,"foo")) …) the outcome (success or failure) of the open-operation will determine, if the condition evaluates to true or false. If now such an operation fails, your program will not be terminated and you might want to learn the reason for failure. This reason will be returned by peek("error") (as a number) or by peek$("error") (as a string)

The table below shows the various error codes; the value returned by peek$("error") explains the nature of the error. Note, that the codes 10,11 and 12 refer to the seek-command.

Table 7.1. Error codes

peek("error")peek$("error")Explanation
2Stream already in useDo not try to open one and the same filenumber twice; rather close it first.
3'x' is not a valid filemodeThe optional filemode argument, which may be passed to the open-function, has an invalid value
4could not open 'foo'The open-call did not work, no further explanation is available.
5reached maximum number of open filesYou have opened more files than your operating system permits.
6cannot open printer: already printing graphicsThe commands open printer and open #1,printer both open a printer (refer to their description for the difference). However, only one can be active at a time; if you try to do both at the same time, you will receive this error.
7could not open line printerWell, it simply did not work.
9invalid stream numberAn attempt to use an invalid (e.g. negative) stream number; example: open(-1,"foo")
10could not position stream x to byte yseek did not work.
11stream x not openYou have tried to seek within a stream, that has not been opened yet.
12seek mode 'x' is none of begin,end,hereThe argument, which has been passed to seek is invalid.

peek("fontheight")

Return the height of the font used within the graphic window. If none is open, this peek will return the height of the last font used or 10, if no window has been opened yet.

peek("screenheight")

Return the height in characters of the window, wherein yabasic runs. If you have not called clear screen yet, this peekwill return 0, regardless of the size of your terminal.

peek("screenwidth")

Return the width in characters of the window, wherein yabasic runs. If you have not called clear screen yet, this peekwill return 0, regardless of the size of your terminal.

peek("secondsrunning")

Return the number of seconds that have passed since the start of yabasic.

peek("millisrunning")

Return the number of milliseconds, that have passed since the start of yabasic.

peek("version")

Return the version number of yabasic, e.g. 2.77. See also the related peek$("version"), which returns nearly the same information (plus the patchlevel) as a string, e.g. "2.77.1".

peek("winheight")

Return the height of the graphic-window in pixels. If none is open, this peek will return the height of the last window opened or 100, if none has been opened yet.

peek("winwidth")

Return the width of the graphic-window in pixels. If none is open, this peek will return the width of the last window opened or 100, if none has been opened yet.

peek("isbound")

Return true, if the executing yabasic-program is part of a standalone program; see the section about creating a standalone-program for details.

peek("version")

Return the version number of yabasic (e.g. 2.72).

peek("last_foreign_function_call_okay")

Check for error: If passing "no_error" to foreign_function_call, any error (e.g. failure to load the specified library), will not terminate your yabasic-program but rather store a descriptive error message away for later retrieval. Later on you may then check peek("last_foreign_function_call_okay") to find out, if something went wrong and retrieve a description with peek$("last_foreign_function_call_error_text").

This peek can be abbreviated as peek("last_frnfn_call_okay")

Example

open "foo" for reading as #1
open "bar" for writing as #2
while not eof(#1)
  poke #2,chr$(peek(#1));
wend
          

This program will copy the file foo byte by byte to bar.

Note, that each peek does something entirely different, and only one has been demonstrated above. Therefore you need to make up examples yourself for all the other peeks.

See also

peek$, poke, open


Name

peek$ — retrieve various internal string-information

Synopsis

print peek$("foo")

Description

The peek$-function has many different and unrelated uses. It is a kind of grab-bag for retrieving all kinds of string information, internal to yabasic; the exact nature of the strings returned be the peek$-function depends on the string passed as an argument.

peek$ always returns a string, however the closely related peek-function exists, which may be used to retrieve numerical information from among the internals of yabasic. Finally note, that some of the values which are retrieved with peek$ may even be changed, using the poke-function.

The following list shows all possible arguments to peek$:

peek$("infolevel")

Returns either "debug", "note", "warning", "error" or "fatal", depending on the current infolevel. This value can be specified with an option on the command line or changed during the execution of the program with the corresponding poke; however, normally only the author of yabasic (me !) would want to change this from its default value "warning".

peek$("textalign")

Returns one of nine possible strings, specifying the default alignment of text within the graphics-window. The alignment-string returned by this peek describes, how the text-command aligns its string-argument with respect to the coordinates supplied. However, this value does not apply, if the text-command explicitly specifies an alignment. Each of these strings is two characters long. The first character specifies the horizontal alignment and can be either l, r or c, which stand for left, right or center. The second character specifies the vertical alignment and can be one of t, b or c, which stand for top, bottom or center respectively.

You may change this value with the corresponding command poke "textalign",…; the initial value is lb, which means the top of the left and the top edge if the text will be aligned with the coordinates, that are specified within the text-command.

peek$("windoworigin")

This peek returns a two character string, which specifies the position of the origin of the coordinate system of the window; this string might be changed with the corresponding command poke "windoworigin",x,y or specified as the argument of the origin command; see there for a detailed description of the string, which might be returned by this peek.

peek$("program_name")

Returns the name of the yabasic-program that is currently executing; typically this is the name, that you have specified on the commandline, but without any path-components. So this peek$ might return foo.yab. As a special case when yabasic has been invoked without the name of a program to be executed this peek will return the literal strings standard input or, when also the option -e has been specified, command line. See also peek$("program_file_name") and peek$("interpreter_path") for related information.

peek$("program_file_name")

Returns the full file-name of the yabasic-program that is currently executing; typically this is the name, that you have specified on the commandline, including any path-components. For the special case, that you have bound your yabasic-program with the interpreter to a single standalone executable, this peek$ will return its name. See also peek$("program_name") and peek$("interpreter_path") for related information.

peek$("interpreter_path")

Return the full file-name of the yabasic-interpreter that is currently executing your program; typically this will end on yabasic or yabasic.exe depending on your platform and the path will be where you installed yabasic. For bound programs (see creating a standalone-program) however, this may be different and will include whatever you specified during the bind-command.

See also peek$("program_name") and peek$("program_file_name") for related information. Employing these, it would be possible for a yabasic-program to start itself: system(peek$("interpreter_path") + " " + peek$("program_file_name")). Of course, in this simple form this would be a bad idea, because this would start concurrent instances of yabasic without end.

peek$("error")

Return a string describing the nature of the last error in an open- or seek-statement. See the corresponding peek("error") for a detailed description.

peek$("library")

Return the name of the library, this statement is contained in. See the import-command for a detailed description or for more about libraries.

peek$("version")

Version of yabasic as a string; e.g. 2.77.1. See also the related peek("version"), which returns nearly the same information (minus the patchlevel) as a number, e.g. 2.77.

peek$("os")

This peek returns the name of the operating system, where your program executes. This can be either windows or unix.

peek$("font")

Return the name of the font, which is used for text within the graphic window; this value can be specified as the third argument to the open window-command.

peek$("env","NAME")

Return the environment variable specified by NAME (which may be any string expression). Which kind of environment variables are available on your system depends, as well as their meaning, on your system; however typing env on the command line will produce a list (for Windows and Unix alike). Note, that peek$("env",...) can be written as peek$("environment",...) too.

peek$("argument")

Return one of the arguments, that have been passed to yabasic at invocation time (the next call will return the the second argument, and so on). E.g. if yabasic has been called like this: yabasic foo.yab bar baz, then the first call to peek$("argument") will return bar. This is because foo.yab is treated as the name of the program to run, whereas bar and baz are considered arguments to this program, which are passed on the command line. The second call to peek$("argument") will return baz. Note, that for windows-users, who tend to click on the icon (as opposed to starting yabasic on the command line), this peekwill mostly return the empty string.

Note, that peek$("argument") can be written as peek$("arguments").

Finally you will want to check out the corresponding function peek("argument").

peek$("last_foreign_function_call_error_text")

Retrieve error text: If passing "no_error" to foreign_function_call, any error (e.g. failure to load the specified library), will not terminate your yabasic-program but rather store a descriptive error message away for later retrieval. Later on you may then check peek("last_foreign_function_call_okay") to find out, if something went wrong and retrieve a description with peek$("last_foreign_function_call_error_text").

This peek can be abbreviated as peek$("last_frnfn_call_error_text")

Example

print "You have supplied these arguments: "
while peek("argument")
  print peek("argument"),peek$("argument")
wend
          

If you save this program in a file foo.yab and execute it via yabasic t.yab a b c (for windows users: please use the command line for this), your will get this output:

3a
2b
1c

See also

peek, poke, open


Name

pi — a constant with the value 3.14159

Synopsis

print pi

Description

pi is 3.14159265359 (well at least for yabasic); do not try to assign to pi (e.g. pi=22/7) this would not only be mathematically dubious, but would also result in a syntax error.

Example

for a=0 to 180
  print "The sine of ",a," degrees is ",sin(a*pi/180)
next a
          

This program uses pi to transform an angle from degrees into radians.

See also

euler


Name

poke — change selected internals of yabasic

Synopsis

poke "foo","bar"
poke "foo",baz
poke #a,"bar"
poke #a,baz

Description

The poke-command may be used to change details of yabasic's behaviour. Like the related function peek, poke does many different things, depending on the arguments supplied.

Here are the different things you can do with poke:

poke 5,a

Write the given byte (a in the example above) to the specified stream (5#a in the example).

See also the related function function peek(1).

poke "dump","filename.dump"

Dump the internal form of your basic-program to the named file; this is only useful for debugging the internals of yabasic itself.

The second argument ("filename.dump" in the example) should be the name of a file, that gets overwritten with the dump, please be careful.

poke "fontheight",12

This poke changes the default fontheight. This can only have an effect, if the fonts given in the commands text or open window do not specify a fontheight on their own.

poke "font","fontname"

This poke specifies the default font. This can only have an effect, if you do not supply a fontname with the commands text or open window.

poke "infolevel","debug"

Change the amount of internal information, that yabasic outputs during execution.

The second argument can be either "debug", "note", "warning", "error" or "fatal". However, normally you will not want to change this from its default value "warning".

See also the related peek$("infolevel").

poke "random_seed",42

Set the seed for the random number generator; if you do this, the ran-function will return the same sequence of numbers every time the program is started.

poke "stdout","some text"

Send the given text to standard output. Normally one would use print for this purpose; however, sending e.g. control characters to your terminal is easier with this poke.

poke "textalign","cc"

This poke changes the default alignment of text with respect to the coordinates supplied within the text-command. However, this value does not apply, if the text-command explicitly specifies an alignment. The second argument ("cc" in the example) must always be two characters long; the first character can be one of l (left), r (right) or c (center); the second character can be either t (top), b (bottom) or c (center); see the corresponding peek$("textalign") for a detailed description of this argument.

poke "windoworigin","lt"

This poke moves the origin of the coordinate system of the window to the specified position. The second argument ("lt" in the example) must always be two characters long; the first character can be one of l (left), r (right) or c (center); the second character can be either t (top), b (bottom) or c (center). Together those two characters specify the new position of the coordinate-origin. See the corresponding peek$("windoworigin") for a more in depth description of this argument.

Example

print "Hello, now you will see, how much work"
print "a simple for-loop involves ..."
input "Please press return " a$
poke "infolevel","debug"
for a=1 to 10:next a
          

This example only demonstrates one of the many pokes, which are described above: The program switches the infolevel to debug, which makes yabasic produce a lot of debug-messages during the subsequent for-loop.

See also

peek, peek$


Name

print — Write to terminal or file

Synopsis

print "foo",a$,b
print "foo",a$,b;
print #a "foo",a$
print #a "foo",a$;
print foo using "##.###"
print reverse "foo"
print at(10,10) a$,b
print @(10,10) a$,b
print color("red","blue") a$,b
print color("magenta") a$,b
print color("green","yellow") at(5,5) a$,b

Description

The print-statement outputs strings or characters, either to your terminal (also known as console) or to an open file.

To understand all those uses of the print-statement, let's go through the various lines in the synopsis above:

print "foo",a$,b

Print the string foo as well as the contents of the variables a$ and b onto the screen, silently adding a newline.

print "foo",a$,b;

(Note the trailing semicolon !) This statement does the same as the one above; only the implicit newline is skipped, which means that the next print-statement will append seamlessly.

print #a "foo",a$

This is the way to write to files. The file with the number a must be open already, an implicit newline is added. Note the file-number #a, which starts with a hash ('#') amd is separated from the rest of the statement by a space only. The file-number (contained in the variable a) must have been returned by a previous open-statement (e.g. a=open("bar")).

print #a "foo",a$;

The same as above, but without the implicit newline.

print foo using "##.###"

Print the number foo with as many digits before and after the decimal dot as given by the number of '#'-signs. See the entries for using and str$ for a detailed description of this format.

print reverse "foo"

As all the print-variants to follow, this form of the print-statement can only be issued after clear screen has been called. The strings and numbers after the reverse-clause are simply printed inverse (compared to the normal print-statement).

print at(10,10) a$,b

Print at the specified (x,y)-position. This is only allowed after clear screen has been called. You may want to query peek$("screenwidth") or peek$("screenheight") to learn the actual size of your screen. You may add a semicolon to suppress the implicit newline.

print @(10,10) a$,b

This is exactly the same as above, however, at may be written as @.

print color("red","blue") at(5,5) a$,b

Print with the specified fore- ("red") and background ("blue") color (or colour). The possible values are "black", "white", "red", "blue", "green", "yellow", "cyan" or "magenta". Again, you need to call clear screen first and add a semicolon if you want to suppress the implicit newline.

print color("magenta") a$,b

You may specify the foreground color only.

print color("green","yellow") a$,b

A color and a position (in this sequence, not the other way around) may be specified at once.

Example

clear screen
columns=peek("screenwidth")
lines=peek("screenheight")
dim col$(7)
for a=0 to 7:read col$(a):next a
data "black","white","red","blue","green","yellow","cyan","magenta"

for a=0 to 2*pi step 0.1
  print colour(col$(mod(i,8))) at(columns*(0.8*sin(a)+0.9)/2,lines*(0.8*cos(a)+0.9)/2) "*"
  i=i+1
next a
          

This example draws a colored ellipse within the text window.


Name

print color — print with color

Synopsis

print color(fore$) text$
print color(fore$,back$) text$

Description

Not a separate command, but part of the print-command; may be included just after print and can only be issued after clear screen has been executed.

color() takes one or two string-arguments, specifying the color of the text and (optionally) the background.

The one or two strings passed to color() can be one of these: "black", "white", "red", "blue", "green", "yellow", "cyan" and "magenta" (which can be abbreviated as "bla", "whi", "red", "blu", "gre", "yel", "cya" and "mag" respectively).

color() can only be used, if clear scren has been issued at least once.

Note, that color() can be written as colour() too.

Example

clear screen
dim col$(7):for a=0 to 7:read col$(a):next a
do
  print color(col$(ran(7)),col$(ran(7))) " Hallo ";
  pause 0.01
loop
data "black","white","red","blue"
data "green","yellow","cyan","magenta"
          

This prints the word " Hallo " in all colors across your screen.


Name

print colour — see print color

Synopsis

print colour(fore$) text$
print colour(fore$,back$) text$

See also

color


Name

putbit — draw a rectangle of pixels encoded within a string into the graphics window

Synopsis

open window 200,200
…
a$=getbit(20,20,50,50)
…
putbit a$,30,30
putbit a$ to 30,30
putbit a$,30,30,"or"

Description

The putbit-command is the counterpart of the getbit$-function. putbit requires a string as returned by the getbit-function. Such a string contains a rectangle from the graphic window; the putbit-function puts such a rectangular region back into the graphic-window.

Note, that the putbit-command currently accepts a fourth argument. However only the string value "or" is supported here. The effect is, that only those pixel, which are set in the string will be set in the graphic window. Those pixels, which are not set in the string, will not change in the window (as opposed to being cleared).

Example


c$="rgb 21,21:0000000000000000000000000000000000000000000000000000000000000032c80000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c8c8ff000032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c8000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"

open window 200,200

do
  x=ran(220)-10
  y=ran(220)-10
  putbit c$,x,y,"transparent"
loop
          

This program uses a precanned string (containing the image of a blue circle with a yellow centre) and draws it repeatedly into the graphic-window. The mode "transparent" ensures, that no pixels will be cleared.

There are two possible values for the third argument of putbit. Both modes differ in the way, they replace (or not) any pixels from the window with pixels from the bitmap having the background colour.

transparent or t

With this mode the pixels from the window will be kept, if the bitmap contains pixels with background colour at this position; i.e. the bitmap is transparent

solid or s

With this mode the pixels from the window will be overpainted with the pixels from the bitmap in any case; i.e. the bitmap is solid

If you omit this argument, the default transparent applies.


Name

putscreen — draw a rectangle of characters into the text terminal

Synopsis

clear screen
…
a$=getscreen$(5,5,10,10)
…
putscreen a$,7,7

Description

The putscreen-command is the counterpart of the getscreen$-function. putscreen requires a string as returned by the getscreen-function. Such a string contains a rectangular detail from the terminal; the putscreen-function puts such a region back into the terminal-window.

Note, that clear screen must have been called before.

Example

clear screen
for a=1 to 200
  print color("red") "Hallo !"; 
  print color("blue") "Welt !";
next a
r$=getscreen$(0,0,20,20)
for x=0 to 60
  putscreen r$,x,0
  sleep 0.1
next x
          

This example prints the string "Hallo !Welt !" all over the screen and then moves a rectangle from one side to the other.

R

ran() — return a random number
read — read data from data-statements
rectangle — draw a rectangle
redim — create an array prior to its first use. A synonym for dim
rem — start a comment
repeat — start a repeat-loop
restore — reposition the data-pointer
return — return from a subroutine or a gosub
reverse — print reverse (background and foreground colors exchanged)
right$() — return (or change) the right end of a string
rinstr() — find the rightmost occurrence of one string within the other
round() — round its argument to the nearest integer
rtrim$() — trim spaces at the right end of a string

Name

ran() — return a random number

Synopsis

print ran()
x=ran(y)

Description

The ran-function returns a random number. If no argument is given, the number returned is in the range from 0 to 1; where only 0 is a possible value; 1 will never be returned. If an argument is supplied, the number returned will be in the range from 0 up to this argument, whereas this argument itself is not a possible return value. Regardless of the range, ran is guaranteed to have exactly 2**30 different return values.

If you call ran multiple times during your program, the sequence of random numbers will be different each time you invoke your program; however, if, e.g. for testing you prefer to always have the same sequence of random numbers you may issue poke "random_seed",123.

Example

clear screen
c=peek("screenwidth")-1
l=peek("screenheight")

dim col$(8)
for a=0 to 7:read col$(a):next a
data "black","white","red","blue","green","yellow","cyan","magenta"

do
  x=ran(c)
  y=l-ran(l*exp(-32*((x/c-1/2)**2)))
  i=i+1
  print color(col$(mod(i,8))) at(x,y) "*";
loop
          

This example will print a colored bell-curve.

See also

int


Name

read — read data from data-statements

Synopsis

read a$,a
…
data "Hello !",7

Description

The read-statement retrieves literal data, which is stored within data-statements elsewhere in your program.

Example

read num
dim col$(num)
for a=1 to num:read col$(a):next a
clear screen
print "These are the colours known to yabasic:\n"
for a=1 to num
  print colour(col$(a)) col$(a)
next a

data 8,"black","white","red","blue"
data "green","yellow","cyan","magenta"
          

This program prints the names of the colors known to yabasic in those very colors.

See also

data, restore


Name

rectangle — draw a rectangle

Synopsis

open window 100,100
rectangle 10,10 to 90,90
rectangle 20,20,80,80
rect 20,20,80,80
box 30,30,70,70
clear rectangle 30,30,70,70
fill rectangle 40,40,60,60
clear fill rectangle 60,60,40,40

Description

The rectangle-command (also known as box or rect, for short) draws a rectangle; it accepts four parameters: The x- and y-coordinates of two facing corners of the rectangle. With the optional clauses clear and fill (which may appear together and in any sequence) the rectangle can be cleared and filled respectively.

Example

open window 200,200
c=1
do 
  for phi=0 to pi step 0.1
    if (c) then 
      rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),100-100*cos(phi)
    else 
      clear rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),100-100*cos(phi)
    endif
    sleep 0.1
  next phi
  c=not c
loop
          

This example draws a nice animated pattern; watch it for a couple of hours, to see how it develops.


Name

redim — create an array prior to its first use. A synonym for dim

Synopsis

See the dim-command.

Description

The redim-command does exactly the same as the dim-command; it is just a synonym. redim has been around in older versions of basic (not even yabasic) for many years; therefore it is supported in yabasic for compatibility reasons.

Please refer to the entry for the dim-command for further information.


Name

rem — start a comment

Synopsis

rem  Hey, this is a comment
#    the hash-sign too (at beginning of line)
// even the double slash
' and the single quote (at beginning of line)
print "Not a comment" #    This is an error !!
print "Not a comment"://   But this is again a valid comment
print "Not a comment" //   even this.
print "Not a comment" rem  and this !

Description

rem introduces a comment (like # or //), that extends up to the end of the line.

Those comments do not even need a colon (':') in front of them; they (rem, #, ' (single quite) and //) all behave alike except for # and ', which may only appear at the very beginning of a line; therefore the fourth example in the synopsis above (print "Not a comment" # This is an error !!) is indeed an error.

Note, that rem is an abbreviation for remark. remark however is not a valid command in yabasic.

Finally note, that a comment introduced with '#' may have a special meaning under unix; see the entry for # for details.

Example

#
rem   comments on data structures
#     are more useful than
//    comments on algorithms.
rem
          

This program does nothing, but in a splendid and well commented way.

See also

#, //


Name

repeat — start a repeat-loop

Synopsis

repeat 
  …
until …

Description

The repeat-loop executes all the statements up to the final until-keyword over and over. The loop is executed as long as the condition, which is specified with the until-clause, becomes true. By construction, the statements within the loop are executed at least once.

Example

x=0
clear screen
print "This program will print the numbers from 1 to 10"
repeat
  x=x+1
  print x
  print "Press any key for the next number, or 'q' to quit"
  if (inkey$="q") break
until x=10
          

This program is pretty much useless, but self-explanatory.

See also

until, break, while, do


Name

restore — reposition the data-pointer

Synopsis

read a,b,c,d,e,f
restore
read g,h,i
restore foo
data 1,2,3
label foo
data 4,5,6

Description

The restore-command may be used to reset the reading of data-statements, so that the next read-statement will read data from the first data-statement.

You may specify a label with the restore-command; in that case, the next read-statement will read data starting at the given label. If the label is omitted, reading data will begin with the first data-statement within your program.

Example

input "Which language (german/english) ? " l$
if (instr("german",l$)>0) then
  restore german
else
  restore english
endif

for a=1 to 3
  read x,x$
  print x,"=",x$
next a

label english
data 1,"one",2,"two",3,"three"
label german
data 1,"eins",2,"zwei",3,"drei"
          

This program asks to select one of those languages known to me (i.e. english or german) and then prints the numbers 1,2 and 3 and their textual equivalents in the chosen language.

See also

read, data, label


Name

return — return from a subroutine or a gosub

Synopsis

gosub foo
…
label foo
…
return

sub bar(baz)
  …
  return quertz
end sub

Description

The return-statement serves two different (albeit somewhat related) purposes. The probably more important use of return is to return control from within a subroutine to the place in your program, where the subroutine has been called. If the subroutine is declared to return a value, the return-statement might be accompanied by a string or number, which constitutes the return value of the subroutine.

However, even if the subroutine should return a value, the return-statement need not carry a value; in that case the subroutine will return 0 or the empty string (depending on the type of the subroutine). Moreover, feel free to place multiple return-statements within your subroutine; it's a nice way of controlling the flow of execution.

The second (but historically first) use of return is to return to the position, where a prior gosub has left off. In that case return may not carry a value.

Example

do
  read a$
  if (a$="") then
    print
    end
  endif
  print mark$(a$)," ";
loop

data "The","quick","brown","fox","jumped"
data "over","the","lazy","dog",""

sub mark$(a$)
  if (instr(lower$(a$),"q")) return upper$(a$)
  return a$
end sub
          

This example features a subroutine mark$, that returns its argument in upper case, if it contains the letter "q", or unchanged otherwise. In the test-text the word quick will end up being marked as QUICK.

The example above demonstrates return within subroutines; please see gosub for an example of how to use return in this context.

See also

sub, gosub


Name

reverse — print reverse (background and foreground colors exchanged)

Synopsis

clear screen
…
print reverse "foo"

Description

reverse may be used to print text in reverse. reverse is not a separate command, but part of the print-command; it may be included just after the print and can only be issued once that clear screen has been issued.

Example

clear screen

print "1 ";
c=3
do
  prim=true
  for a=2 to sqrt(c)
    if (frac(c/a)=0) then
      prim=false
      break
    endif
  next a
  if (prim) then
    print
    print reverse c;
  else
    print c;
  endif
  print " ";
  c=c+1
loop
          

This program prints numbers from 1 on and marks each prime number in reverse.


Name

right$() — return (or change) the right end of a string

Synopsis

print right$(a$,2)
right$(b$,2)="baz"

Description

The right$-function requires two arguments (a string and a number) and returns the part from the right end of the string, whose length is specified by its second argument. So, right$ simply returns the requested number of chars from the right end of the given string.

Note, that the right$-function can be assigned to, i.e. it may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the right$-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.

Example

print "Please enter a length either in inch or centimeter"
print "please add 'in' or 'cm' to mark the unit."
input "Length: " a$
if (right$(a$,2)="in") then
   length=val(a$)*2.56
elsif (right$(a$,2)="cm") then
   length=val(a$)
else
   error "Invalid input: "+a$
endif
          

This program allows the user to enter a length qualified with a unit (either inch or centimeter).

This second example demonstrates the capability to assign to the right$-function.

a$="Heiho World !"
print a$
right$(a$,7)="dwarfs."
print a$

See also

right$ and mid$


Name

rinstr() — find the rightmost occurrence of one string within the other

Synopsis

pos=rinstr("Thequickbrownfox","equi")
pos=rinstr(a$,b$,x)

Description

The rinstr-function accepts two string-arguments and tries to find the second within the first. However, unlike the instr, the rinstr-function finds the rightmost (or last) occurrence of the string; whereas the instr-function finds the leftmost (or first) occurrence. In any case however, the position is counted from the left.

If you supply a third, numeric argument to the rinstr-function, it will be used as a starting point for the search. Therefore rinstr("abcdeabcdeabcde","e",8) will return 5, because the search for an "e" starts at position 8 and finds the first one at position 5.

Example

print rinstr("foofoofoobar","foo")
          

This simple example will print 7, because it finds the rightmost among the three occurrences of foo within the string. Note, that

print instr("foofoofoobar","foo")

would have printed 1.

See also

instr


Name

round() — round its argument to the nearest integer

Synopsis

print round(x)

Description

The found-function returns the nearest integer (e.g. 3.0 for an argument of 2.6). An argument with a fractional part of 0.5 (e.g. 2.5) represents an edge case, as such an argument has the same distance to two numbers, 3.0 and 2.0 in the example; this ambiguity is resolved by rounding away from zero and returning 3.0. By the same rule round(-2.5) returns -3.0; so you see, that round(x) always equals round(-x).

Example

print round(2.3), round(2.5), round(2.7)
print round(2), round(-2)
print int(-2.3),round(-2.5), round(-2.7)
          

These examples return in order 2 3 3, then 2 -2 and finally 2 -3 -3.

See also

ceil, floor, int, frac


Name

rtrim$() — trim spaces at the right end of a string

Synopsis

a$=rtrim$(b$)

Description

The rtrim$-function removes all whitespace from the right end of a string and returns the result.

Example

open 1,"foo"
dim lines$(100)
l=1
while not eof(1)
  input #1 a$
  a$=rtrim$(a$)
  if (right$(line$,1)="\\") then
    line$=line$+" "+a$
  else
    lines$(l)=line$
    l=l+1
    line$=a$
  endif
end while
print "Read ",l," lines"
          

This example reads the file foo allowing for continuation lines, which are marked by a \, which appears as the last character on a line. For convenience whitespace at the right end of a line is trimmed with rtrim.

See also

ltrim$, trim$

S

screen — as clear screen clears the text window
seek() — change the position within an open file
sig() — return the sign of its argument
sin() — return the sine of its single argument
shl() — shift its argument bitwise to the left
shr() — shift its argument bitwise to the right
sleep — pause, sleep, wait for the specified number of seconds
split() — split a string into many strings
sqr() — compute the square of its argument
sqrt() — compute the square root of its argument
static — preserves the value of a variable between calls to a subroutine
step — specifies the increment step in a for-loop
str$() — convert a number into a string
sub — declare a user defined subroutine
switch — select one of many alternatives depending on a value
system() — hand the name of an external command over to your operating system and return its exitcode
system$() — hand the name of an external command over to your operating system and return its output

Name

screen — as clear screen clears the text window

Synopsis

clear screen

Description

The keyword screen appears only within the sequence clear screen; please see there for a description.

See also

clear screen


Name

seek() — change the position within an open file

Synopsis

open 1,"foo"
seek #1,q
seek #1,x,"begin"
seek #1,y,"end"
seek #1,z,"here"

Description

The seek-command changes the position, where the next input (or peek) statement will read from an open file. Usually files are read from the beginning to the end sequentially; however sometimes you may want to depart from this simple scheme. This can be done with the seek-command, allowing you to change the position, where the next piece of data will be read from the file.

seek accepts two or three arguments: The first one is the number of an already open file. The second one is the position where the next read from the file will start. The third argument is optional and specifies the the point from where the position (the second argument) will count. It can be one of:

begin

Count from the beginning of the file.

end

Count from the end of the file.

here

Count from the current position within the file.

Example

open #1,"count.dat","w"
for a=1 to 10
  print #1,"00000000";
  if (a<10) print #1,";";
next a

dim count(10)
do
  x=int(ran(10))
  i=i+1
  if (mod(i,1000)=0) print ".";
  count(x)=count(x)+1
  curr$=right$("00000000"+str$(count(x)),8)
  seek #1,9*x,"begin"
  print #1,curr$;
loop
          

This example increments randomly one of ten counters (in the array count()); however, the result is always kept and updated within the file count.dat, so even in case of an unexpected interrupt, the result will not be lost.

See also

tell, open, print, peek


Name

sig() — return the sign of its argument

Synopsis

a=sig(b)

Description

Return +1, -1 or 0, if the single argument is positive, negative or zero.

Example

clear screen
dim c$(3):c$(1)="red":c$(2)="white":c$(3)="green"
do
  num=ran(100)-50
  print color(c$(2+sig(num))) num
loop
          

This program prints an infinite sequence of random number; positive numbers are printed in green, negative numbers are printed red (an exact zero would be printed white). (With a little extra work, this program could be easily extended into a brokerage system)

See also

abs, int, frac


Name

sin() — return the sine of its single argument

Synopsis

y=sin(angle)

Description

The sin-function expects an angle (in radians, not degrees) and returns its sine.

Example

open window 200,200
new curve
for phi=0 to 2*pi step 0.1
  line to 100+90*sin(phi),100+90*cos(phi)
next phi
close curve
          

This program draws a circle (ignoring the existence of the circle-command).

See also

asin, cos


Name

shl() — shift its argument bitwise to the left

Synopsis

print shl(0b11001,8)	    

Description

The shl-function (shl stands for shift left) treats its first argument as a binary number and shifts it to the left as specified by its second argument, filling up the gaps with zeroes. So bin$(shl(0b11011,4)) returns 110110000 (the example uses bin$ and a number with base 2).

Please note: as the argument of the function is converted to a 32-bit integer, all results are also confined to this range.

Example

print "Some powers of two:"
for i=0 to 5
  print shl(1,i)
next i
          

This will print the powers of two from 1 to 32, because the left-shift operation is equivalent to a multiplication with two.

See also

and, or, eor, bitnot, shr


Name

shr() — shift its argument bitwise to the right

Synopsis

print shr(0b110010000,4)	    

Description

The shr-function (shr stands for shift right) treats its first argument as a binary number and shifts it to the right as specified by its second argument; the rightmost binary digits are discarded during this operation. So bin$(shr(0b1101100,2)) returns 11011 (the example uses bin$ and a number with base 2).

Please note: as the argument of the function is converted to a 32-bit integer, all results are also confined to this range.

Example

print "Some powers of two:"
for i=0 to 5
  print shr(32,i)
next i
          

This will print the powers of two from 32 downto 1, because the right-shift operation is equivalent to a division by two (discarding any fractional part).

See also

and, or, eor, bitnot, shl


Name

sleep — pause, sleep, wait for the specified number of seconds

Synopsis

sleep 4

Description

The sleep-command has many different names: You may write pause, sleep or wait interchangeably; whatever you write, yabasic will always do exactly the same.

Therefore you should refer to the entry for the pause-function for further information.


Name

split() — split a string into many strings

Synopsis

dim w$(10)
…
num=split(a$,w$())
num=split(a$,w$(),s$)

Description

The split-function requires a string (containing the text to be split), a reference to a string-array (which will receive the resulting strings, i.e. the tokens) and an optional string (with a set of characters, at which to split, i.e. the delimiters).

The split-function regards its first argument (a string) as a list of tokens separated by delimiters and it will store the list of tokens within the array-reference you have supplied. Note, that the array, which is passed as a reference (w$() in the synopsis), will be resized accordingly, so that you don't have to figure out the number of tokens in advance. The element at position zero (i.e. w$(0)) will not be used.

normally (i.e. if you omit the third, which is the delimiter-argument) the function will regard space or tab as delimiters for tokens; however by supplying a third argument, you may split at any single of the characters within this string. E.g. if you supply ":;" as the third argument, then colon (:) or semicolon (;) will delimit tokens.

Note, that a sequence of separator-characters will produce a sequence of empty tokens; that way, the number of tokens returned will always be one plus the number of separator characters contained within the string. Refer to the closely related token-function, if you do not like this behaviour. In some way, the split-function focuses on the separators (other than the token-function, which focuses on the tokens), hence its name.

The second argument is a reference on a string-array, where the tokens will be stored; this array will be expanded (or shrunk) to have room for all tokens, if necessary.

The first argument finally contains the text, that will be split into tokens. The split-function returns the number of tokens that have been found.

Please see the examples below for some hints on the exact behaviour of the split-function and how it differs from the token-function:

Example

print "This program will help you to understand, how the"
print "split()-function exactly works and how it behaves"
print "in certain special cases."
print
print "Please enter a line containing tokens separated"
print "by either '=' or '-'"
dim t$(10)
do
  print 
  input "Please enter a line: " l$
  num=split(l$,t$(),"=-")
  print num," Tokens: ";
  for a=1 to num
    if (t$(a)="") then
      print "(EMPTY)";
    else 
      print t$(a);
    endif
    if (a<num) print ","; 
  next a
  print
loop
          

This program prints the following output:

Please enter a line: a
1 Tokens: a

Please enter a line:
0 Tokens:

Please enter a line: ab
1 Tokens: ab

Please enter a line: a=b
2 Tokens: a,b

Please enter a line: a-
2 Tokens: a,(EMPTY)

Please enter a line: a-=
3 Tokens: a,(EMPTY),(EMPTY)

Please enter a line: =a-
3 Tokens: (EMPTY),a,(EMPTY)

Please enter a line: a=-b
3 Tokens: a,(EMPTY),b

Please enter a line: a--b-
4 Tokens: a,(EMPTY),b,(EMPTY)

Please enter a line: -a==b-c==
7 Tokens: (EMPTY),a,(EMPTY),b,c,(EMPTY),(EMPTY)

See also

token


Name

sqr() — compute the square of its argument

Synopsis

a=sqr(b)

Description

The sqr-function computes the square of its numerical argument (i.e. it multiplies its argument with itself).

Example

for a=1 to 10
  print a,sqr(a),a**2
next a
          

As you may see from the output, sqr can be written as **2 (or ^2) too.

See also

sqrt, **, ^


Name

sqrt() — compute the square root of its argument

Synopsis

to be written

Description

The sqrt-function computes the square root of its numerical argument.

Example

for a=1 to 5
  print a,sqrt(a),a**(1/2)
next a
          

As you may see from the output, sqrt can be written as **(1/2) (or ^(1/2)) too.

See also

sqr, **, ^


Name

static — preserves the value of a variable between calls to a subroutine

Synopsis

sub foo()

  static a

  …

end sub 

Description

The static keyword can be used within subroutines to mark variables as static. This has two effects: First, the variable is local to the subroutine, i.e. its value is not know outside the subroutine (this is the effect of the local keyword). Second, the static-keyword arranges things, so that the variable keeps its value between invocations of the subroutine (this is different from the local-keyword).

Example

foo()
foo()
foo()

sub foo()
  static a
  local b
  a=a+1
  b=b+1
  print a,b
end sub
          

This program shows the difference between static and local variables within a subroutine; it produces this output:

1 1
2 1
3 1

The output shows, that the static variable a keeps its value between subroutine calls, whereas b is initialized with the value 0 at every call to the subroutine foo.

See also

sub, local


Name

step — specifies the increment step in a for-loop

Synopsis

for a=1 to 10 step 3
  …
next a

Description

Specify, by which amount the loop-variable of a for-loop will be incremented at each step.

The step (as well as the lower and upper bound) are computed anew in each step; this is not common, but possible, as the example below demonstrates.

Example

for x=1 to 1000 step y
  y=x+y
  print x," ",y," ";
next x
print
          

This program computes the fibonacci numbers between 1 and 1000.

See also

for


Name

str$() — convert a number into a string

Synopsis

a$=str$(a)
b$=str$(x,"##.###")
b$=str$(x,"###,###.##")
b$=str$(x,"###,###.##","_.")

Description

The str$-function accepts a numeric argument and returns it as a string. This conversion between number and string can be controlled with the optional third argument (the format argument). See the following table of examples to learn about valid values of this argument. Note, that those examples fall in one of two categories: C-style and basic-style; the first 4 examples in the table below are C-style, the rest of the examples are basic-style. For more information on the C-style formats, you may refer to your favorite documentation on the C programming language. The basic-style formats are much simpler, they just depict the desired output, marking digits with '#'; groups of (usually three) digits may be separated with colons (','), the decimal dot must be marked by a literal dot ('.'). Moreover these characters (colons and dot) may be replaced by other characters to satisfy the needs of non-english (e.g. german) languages; see the examples below.

Note, that for clarity, each space in the result has been replaced by the letter 'x', because it would be hard to figure out, how many spaces are produced exactly otherwise.

Table 7.2. Examples for the format argument

Example stringResult for converting 1000*piDescription
%g3141.59Internally yabasic uses double precision, so its numbers can be formatted with the %g format specifier.
%2.5f3141.59265The '2' determines the minimum length of the output; but if needed (as in the example) the output can be longer. The '5' is the number of digits after the decimal point.
%12.5fxx3141.59265Two spaces (which appear as 'x') are added to pad the output to the requested length of 12 characters.
%012.5g0000003141.6The 'g' requests, that the precision ('5') specifies the overall number of digits (before and after the decimal point).
%-12.5f3141.59265xxThe '-' requests the output to be left-centered (therefore the filling space appears at the right).
#####.##x3141.59Each '#' specifies a digit (either before or after the dot), the '.' specifies the position of the dot. As 1000*pi does not have enough digits, the 5 requested digits before the dot are filled up with a space (which shows up as an 'x').
##,###.##x3,141.59Nearly the same as above, but the colon from the format shows up within the result.
##,###.## and an additional argument of ".,"x3.141,59Similar to the example above, but colon and dot are replaced with dot and colon respectively.
##,###.## and an additional argument of "_,"x3_141,59Similar to the example above, but colon and dot are replaced with underscore and colon respectively.
#####x3142The format string does not contain a dot, and therefore the result does not have any fractional digits.
##.#####.###As 1000*pi has 4 digits in front of the decimal dot and the format only specifies 2, yabasic does not know what to do; therefore it chooses just to reproduce the format string.

Example

do
  input "Please enter a format string: " f$
  a$=str$(1000*pi,f$)
  for a=1 to len(a$)
    if (mid$(a$,a,1)=" ") mid$(a$,a,1)="x"
  next a
  print a$
loop
          

This is the program, that has been used to get the results shown in the table above.

See also

print, using


Name

sub — declare a user defined subroutine

Synopsis

foo(2,"hello")

…

sub foo(bar,baz$)
  …
  return qux
  …
end sub

Description

The sub-keyword starts the definition of a user defined subroutine. With user defined subroutines you are able to somewhat extend yabasic with your own commands or functions. A subroutine accepts arguments (numbers or strings) and returns a number or a string (however, you are not required to assign the value returned to a variable).

The name of the subroutine follows after the keyword sub. If the name (in the synopsis: foo) ends on a '$', the subroutine should return a string (with the return-statement), otherwise a number.

After the name of the subroutine yabasic requires a pair of braces; within those braces you may specify a list of parameters, for which values can (but need not) be included when calling the subroutine. If you omit one of those parameters when calling such a subroutine, it assumes the value zero (for numeric parameters) or the empty string (for string-parameters). However from the special variable numparams you may find out, how many arguments have really been passed when calling the subroutine.

Parameters of a subroutine are always local variables (see the keyword local for more explanation).

From within the subroutine you may return any time with the keyword return; along with the return-keyword you may specify the return value. Note that more than one return is allowed within a single subroutine.

Finally, the keyword end sub ends the subroutine definition. Note, that the definition of a subroutine need not appear within the program before the first call to this sub.

Note

As braces have two uses in yabasic (i.e. for supplying arguments to a subroutine as well as to list the indices of an array). yabasic can not tell apart an array from a subroutine with the same name. Therefore you cannot define a subroutine with the same name as an array !

Example

p=2
do 
  if (is_prime(p)) print p
  p=p+1
loop

sub is_prime(a)
  local b
  for b=2 to sqrt(a)
    if (frac(a/b)=0) return false
  next b
  return true
end sub
          

This example is not the recommended way to compute prime numbers. However it gives a nice demonstration of using a subroutine.

See also

local, static, peek


Name

switch — select one of many alternatives depending on a value

Synopsis

switch a
  case 1
  case 2
  …
end switch

…

switch a$
  case "a"
  case "b"
end switch

Description

The switch-statement selects one of many codepaths depending on a numerical or string expression. I.e. it takes an expression (either numeric or string) and compares it with a series of values, each wrapped within a case-clause. If the expression equals the value given in a case-clause, the subsequent statements are executed.

The default-clause allows one to specify commands, which should be executed, if none of case-clauses matches.

Note, that many case-clauses might be clustered (e.g. case "a":case "b":case "c"). Or put another way: You need a break-statement at the end of a case-branch, if you do not want to run into the next case.

Example

input "Please enter a single digit: " n
switch n
  case 0:print "zero":break
  case 1:print "one":break
  case 2:print "two":break
  case 3:print "three":break
  case 4:print "four":break
  case 5:case 6: case 7:case 8:case 9
    print "Much !":break
  default:print "Hey ! That was more than a single digit !"
end switch 
          

This example translates a single digit into a string; note, how the cases 5 to 7 are clustered.

See also

switch, case, break


Name

system() — hand the name of an external command over to your operating system and return its exitcode

Synopsis

ret=system("foo")
system("bar")

Description

The system-command accepts a single string argument, which specifies a command to be executed. The function will return the exitcode of the command; its output (if any) will be lost.

Example

print "Please enter the name of the file, that should be deleted."
input f$
if (system("rm "+f$+" >/dev/null 2>&1")) then
  print "Error !"
else
  print "okay."
endif
          

This program is Unix-specific: It uses the Unix-command rm to remove a file.

See also

system$


Name

system$() — hand the name of an external command over to your operating system and return its output

Synopsis

print system$("dir")

Description

The system$-command accepts a single string argument, specifying a command, that can be found and executed by your operating system. It returns the output of this command as one big string.

Example

input "Please enter the name of a directory: " d$
print
print "This is the contents of the '"+d$+"':"
print system$("dir "+d$)
          

This example lists the contents of a directory, employing the dir-command (which is about the only program, that is known under Unix as well as Windows).

See also

system, chomp

T

tan() — return the tangent of its argument
tell — get the current position within an open file
text — write text into your graphic-window
then — tell the long from the short form of the if-statement
time$ — return a string containing the current time
to — this keyword appears as part of other statements
token() — split a string into multiple strings
triangle — draw a triangle
trim$() — remove leading and trailing spaces from its argument
true — a constant with the value of 1

Name

tan() — return the tangent of its argument

Synopsis

foo=tan(bar)

Description

The tan-function computes the tangent of its arguments (which should be specified in radians).

Example

for a=0 to 45
  print tan(a*pi/180)
next a
          

This example simply prints the tangent of all angles between 0 and 45 degrees.

See also

atan, sin


Name

tell — get the current position within an open file

Synopsis

open #1,"foo"
  …
position=tell(#1)

Description

The tell-function requires the number of an open file as an argument. It returns the position (counted in bytes, starting from the beginning of the file) where the next read will start.

Example

open #1,"foo","w"
print #1 "Hello World !"
close #1

open #1,"foo"
seek #1,0,"end"
print tell(#1)
close 1
          

This example (mis)uses tell to get the size of the file. The seek positions the file pointer at the end of the file, therefore the call to tell returns the total length of the file.

See also

tell, open


Name

text — write text into your graphic-window

Synopsis

text x,y,"foo"
text x,y,"foo","lb"
text x,y,"foo","cc","font"
text x,y,"foo","font","rt"

Description

The text-commands displays a text-string (the third argument) at the given position (the first two arguments) within an already opened window. The font to be used can be optionally specified as either the fourth or fifth argument ("font" in the example above). A font specified this way will also be used for any subsequent text-commands, as long as they do not specify a font themselves.

The fourth or fifth optional argument ("lb" in the example above) can be used to specify the alignment of the text with respect to the specified position. This argument is always two characters long: The first character specifies the horizontal alignment and can be either l, r or c, which stand for left, right or center. The second character specifies the vertical alignment and can be one of t, b or c, which stand for top, bottom or center respectively. If you omit this alignment argument, the default "lb" applies; however this default may be changed with poke "textalign","xx"

Example

open window 500,200
clear screen
data "lt","lc","lb","ct","cc","cb","rt","rc","rb"
for a=1 to 9
  read align$	
  print "Alignment: ",align$
  line 50*a-15,100,50*a+15,100
  line 50*a,85,50*a,115
  text 50*a,100,"Test",align$
  inkey$ 
next a
          

This program draws nine crosses and writes the same text at each; however it goes through all possible nine alignment strings, showing their effect.


Name

then — tell the long from the short form of the if-statement

Synopsis

if (a<b) then
  …
endif

Description

The keyword then is part of the if-statement; please see there for further explanations. However, not every if-statement requires the keyword then: If the keyword then is present, the if-clause may extend over more than one line, and the keyword endif is required to end it. If the keyword then is not present, the if-statement extends up to the end of the line, and any endif would be an error.

Example

if (1<2) then 
  print "Hello ";
endif

if (2<3) print "world"
if (2<1)
  print "!"
          

This example prints Hello world. Note, that no exclamation mark (!) is printed, which might come as a surprise and may be changed in future versions of yabasic.

See also

if


Name

time$ — return a string containing the current time

Synopsis

print time$
print time$()

Description

The time$ function returns the current time in four fields separated by hyphens '-'. The fields are:

  • The current hour in the range from 0 to 23, padded with zeroes (e.g. 00 or 04) to a length of two characters.

  • The number of minutes, padded with zeroes.

  • The number of seconds, padded with zeroes.

  • The number of seconds, that have elapsed since the program has been started. This value increases as long as your program runs and is therefore unbound and not padded with zeroes.

At the time of writing this documentation, time$ returns 22-58-53-0. Note, that the first three of the four fields returned by time$ have a fixed width; therefore it is easy to extract some fields with the usual string-functions mid$ (and others).

Example

print "Hello it is ",time$
print "An empty for-loop with ten million iterations takes ";
for a=1 to 10000000:next a
print "Now it is ",time$
print peek("secondsrunning")," seconds have passed."
          

This program benchmarks the for-loop; however, it does not use the fourth field of the string returned by time$, because that string wraps around every 60 seconds; rather the peek "secondsrunning" is queried.

See also

date


Name

to — this keyword appears as part of other statements

Synopsis

for a=1 to 100 step 2
  …
next a

line x,y to a,b

Description

The to-keyword serves two purposes (which are not related at all):

  • within for-statements, to specify the upper bound of the loop.

  • Within any graphical command (e.g. line), that requires two points (i.e. four numbers) as arguments, a comma ',' might be replaced with the keyword to. I.e. instead of 100,100,200,200 you may write 100,100 to 200,200 in such commands.

Example

Please see the command listed under "See also" for examples.

See also

for, line, rectangle


Name

token() — split a string into multiple strings

Synopsis

dim w$(10)
…
num=token(a$,w$())
num=token(a$,w$(),s$)

Description

The token-function accepts a string (containing the text to be split), a reference to a string-array (which will receive the resulting strings, i.e. the tokens) and an optional string (with a set of characters, at which to split, i.e. the delimiters).

The token-function regards its first argument as a list of tokens separated by delimiters and it will store the list of tokens within the array-reference that has been supplied. Note, that the array, which is passed as a reference (w$() in the synopsis), will be resized accordingly, so that you don't have to figure out the number of tokens in advance. The element at position zero (i.e. w$(0)) will not be used.

Normally (i.e. if you omit the third, the delimiter-argument) the function will regard space or tab as delimiters for tokens; however by supplying a third argument, you may split at any single of the characters within this string. E.g. if you supply ":;" as the third argument, then colon (:) or semicolon (;) will delimit tokens.

Note, that token will never produce empty tokens, even if two or more separators follow in sequence. Refer to the closely related split-function, if you do not like this behaviour. In some way, the token-function focuses on the tokens and not on the separators (other than the split-function, which focuses on the separators).

The second argument is a reference on a string-array, where the tokens will be stored; this array will be expanded (or shrunk) as necessary to have room for all tokens.

The first argument finally contains the text, that will be split into tokens. The token-function returns the number of tokens, that have been found.

Please see the examples below for some hints on the exact behaviour of the token-function and how it differs from the split-function:

Example

print "This program will help you to understand, how the"
print "token()-function exactly works and how it behaves"
print "in certain special cases."
print
print "Please enter a line containing tokens separated"
print "by either '=' or '-'"
dim t$(10)
do
  print 
  input "Please enter a line: " l$
  num=token(l$,t$(),"=-")
  print num," Tokens: ";
  for a=1 to num
    if (t$(a)="") then
      print "(EMPTY)";
    else 
      print t$(a);
    endif
    if (a<num) print ","; 
  next a
  print
loop
          
This program prints the following output:

Please enter a line: a
1 Tokens: a

Please enter a line:
0 Tokens:

Please enter a line: ab
1 Tokens: ab

Please enter a line: a=b
2 Tokens: a,b

Please enter a line: a-
1 Tokens: a

Please enter a line: a-=
1 Tokens: a

Please enter a line: =a-
1 Tokens: a

Please enter a line: a=-b
2 Tokens: a,b

Please enter a line: a--b-
2 Tokens: a,b

Please enter a line: -a==b-c==
3 Tokens: a,b,c

See also

split


Name

triangle — draw a triangle

Synopsis

open window 100,100
triangle 100,100,50,50,100,50
fill triangle 50,100,100,50,200,200
clear fill triangle 20,20,10,10,200,200

Description

The triangle-command draws a triangle; it requires 6 parameters: The x- and y-coordinates of the three points making up the triangle. With the optional keywords clear and fill (which may appear both and in any sequence) the triangle can be cleared and filled respectively.

Example

open window 200,200
do 
  phi=phi+0.2
  i=i+2
  color mod(i,255),mod(85+2*i,255),mod(170+3*i,255)
  dx=100*sin(phi):dy=20*cos(phi)
  fill triangle 100+20*sin(phi),100+20*cos(phi),100-20*sin(phi),100-20*cos(phi),100-80*cos(phi),100+80*sin(phi)
  sleep 0.1
loop
          

This example draws a colored triangles until you get exhausted.


Name

trim$() — remove leading and trailing spaces from its argument

Synopsis

a$=trim$(b$)

Description

The trim$-function removes all whitespace from the left and from the right end of a string and returns the result. Calling trim$ is equivalent to calling rtrim$(ltrim$()).

Example

do
  input "Continue ? Please answer yes or no: " a$
  a$=lower$(trim$(a$))
  if (len(a$)>0 and a$=left$("no",len(a$)) exit
loop
          

This example asks for an answer (yes or no) and removes spaces with trim$ to make the comparison with the string "no" more bulletproof.

See also

ltrim$, rtrim$


Name

true — a constant with the value of 1

Synopsis

okay=true

Description

The constant true can be assigned to variables which will later appear in conditions (e.g. an if-statement.

true may also be written as TRUE or even TrUe.

Example

input "Please enter a string of all upper letters: " a$
if (is_upper(a$)) print "Okay"

sub is_upper(a$)
  if (a$=upper$(a$)) return true
  return false
end sub
          

See also

false

U

until — end a repeat-loop
upper$() — convert a string to upper case
using — Specify the format for printing a number

Name

until — end a repeat-loop

Synopsis

repeat 
  …
until …

Description

The until-keyword ends a loop, which has been introduced by the repeat-keyword. until requires an expression (see here for details) as an argument; the loop will continue until this condition evaluates to true.

Example

c=1
s=1
repeat
  l=c
  s=-(s+sig(s))
  c=c+1/s
  print c
until abs(l-c)<0.000001
          

This program calculates the sequence 1/1-1/2+1/3-1/4+1/5-1/6+1/7-1/8+ … ; please let me know, if you know against which value this converges.

See also

repeat


Name

upper$() — convert a string to upper case

Synopsis

u$=upper$(a$)

Description

The upper$-function accepts a single string argument and converts it to all upper case.

Example

line input "Please enter a sentence without the letter 'e': " l$
p=instr(upper$(l$),"E")
if (p) then
  l$=lower$(l$)
  mid$(l$,p,1)="E"
  print "Hey, you are wrong, see here!"
  print l$
else
  print "Thanks."
endif
          

This program asks for a sentence and marks the first (if any) occurrence of the letter 'e' by converting it to upper case (in contrast to the rest of the sentence, which is converted to lower case).

See also

lower$


Name

using — Specify the format for printing a number

Synopsis

print a using "##.###"
print a using("##.###",",.")

Description

The using-keyword may appear as part of the print-statement and specifies the format (e.g. the number of digits before and after the decimal dot), which should be used to print the number.

The possible values for the format argument ("##.###" in the synopsis above) are described within the entry for the str$-function; especially the second line in the synopsis (print a using("##.###",",.")) will become clear after referring to str$. In fact the using clause is closely related to the str$-function; the former can always be rewritten using the latter; i.e. print foo using bar$ is always equivalent to print str$(foo,bar$). Therefore you should check out str$ to learn more.

Example

for a=1 to 10
  print sqrt(ran(10000*a)) using "#########.#####"
next a
          

This example prints a column of square roots of random number, nicely aligned at the decimal dot.

See also

print, str$

V

val() — converts a string to a number

Name

val() — converts a string to a number

Synopsis

x=val(x$)

Description

The val-function checks, if the start of its string argument forms a floating point number and then returns this number. The string therefore has to start with digits (only whitespace in front is allowed), otherwise the val-function returns zero.

Example

input "Please enter a length, either in inches (in) or centimeters (cm) " l$
if (right$(l$,2)="in") then
  l=val(l$)*2.51
else
  l=val(l$)
print "You have entered ",l,"cm."
          

This example queries for a length and checks, if it has been specified in inches or centimeters. The length is then converted to centimeters.

See also

str$

W

wait — pause, sleep, wait for the specified number of seconds
wend — end a while-loop
while — start a while-loop
window origin — move the origin of a window

Name

wait — pause, sleep, wait for the specified number of seconds

Synopsis

wait 4

Description

The wait-command has many different names: You may write pause, sleep or wait interchangeably; whatever you write, yabasic will always do exactly the same.

Therefore you should refer to the entry for the pause-function for further information.


Name

wend — end a while-loop

Synopsis

while a<b
  …
wend

Description

The wend-keyword marks the end of a while-loop. Please see the while-keyword for more details.

wend can be written as end while or even end-while.

Example

line input "Please enter a sentence: " a$
p=instr(a$,"e")
while p
  mid$(a$,p,1)="E"
  p=instr(a$,"e")
wend
print a$
          

This example reads a sentence and converts every occurrence of the letter e into uppercase (E).

See also

while (which is just the following entry).


Name

while — start a while-loop

Synopsis

while …
  …
wend

Description

The while-keyword starts a while-loop, i.e. a loop that is executed as long as the condition (which is specified after the keyword while) evaluates to true.

Note, that the body of such a while-loop will not be executed at all, if the condition following the while-keyword is not true initially.

If you want to leave the loop prematurely, you may use the break-statement.

Example

open #1,"foo"
while !eof(1)
  line input #1 a$
  print a$
wend
          

This program reads the file foo and prints it line by line.

See also

until, break, wend, do


Name

origin — move the origin of a window

Synopsis

open window 200,200
origin "cc"

Description

The origin-command applies to graphic windows and moves the origin of the coordinate system to one of nine point within the window. The normal position of the origin is in the upper left corner of the window; however in some cases this is inconvenient and moving the origin may save you from subtracting a constant offset from all of your coordinates.

However, you may not move the origin to an arbitrary position; in horizontal position there are only three positions: left, center and right, which are decoded by the letters l, c and r. In vertical position the allowed positions are top, center and bottom; encoded by the letters t, c and b. Taking the letters together, you arrive at a string, which might be passed as an argument to the command; e.g. "cc" or "rt".

Example

100,100
open window 200,200
window origin "cc"
circle 0,0,60
          

This example draws a circle, centered at the center of the window.

See also

open window

X

xor() — compute the exclusive or

Name

xor() — compute the exclusive or

Synopsis

x=xor(a,b)

Description

The xor-function computes the bitwise exclusive or of its two numeric arguments. To understand the result, both arguments should be viewed as binary numbers (i.e. a sequence of digits 0 and 1); a bit of the result will then be 1, if exactly one argument has a 1 and the other has a 0 at this position in their binary representation.

Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to and.

Example

print xor(7,4)
          

This will print 3. This result is obvious, if you note, that the binary representation of 7 and 4 are 111 and 100 respectively; this will yield 011 in binary representation or 2 as decimal.

The eor-function is the same as the xor-function; both are synonymous; however they have each their own description, so you may check out the entry of eor for a slightly different view.

See also

and, or, eor, bitnot

Special characters

# — either a comment or a marker for a file-number
// — starts a comment
@ — synonymous to at
: — separate commands from each other
; — suppress the implicit newline after a print-statement
** or ^ — raise its first argument to the power of its second

Name

# — either a comment or a marker for a file-number

Synopsis

# This is a comment, but the line below not !
open #1,"foo"

Description

The hash ('#') has two totally unrelated uses:

  • A hash might appear in commands related with file-io. yabasic uses simple numbers to refer to open files (within input, print, peek or eof). In those commands the hash may precede the number, which species the file. Please see those commands for further information and examples; the rest of this entry is about the second use (as a comment).

  • As the very first character within a line, a hash introduces comments (similar to rem).

'#' as a comment is common in most scripting languages and has a special use under Unix: If the very first line of any Unix-program begins with the character sequence '#!' ("she-bang", no spaces allowed), the rest of the line is taken as the program that should be used to execute the script. I.e. if your yabasic-program starts with '#!/usr/local/bin/yabasic', the program /usr/local/bin/yabasic will be invoked to execute the rest of the program. As a remark for windows-users: This mechanism ensures, that yabasic will be invoked to execute your program; the ending of the file (e.g. .yab) will be ignored by Unix.

Example

# This line is a valid comment
print "Hello " : # But this is a syntax error, because
print "World!" : # the hash is not the first character !
          

Note, that this example will produce a syntax error and is not a valid program !

See also

input, print, peek or eof, //, rem


Name

// — starts a comment

Synopsis

//  This is a comment !

Description

The double-slash ('//') is (besides REM and '#') the third way to start a comment. '//' is the latest and greatest in the field of commenting and allows yabasic to catch up with such cool languages like C++ and Java.

Example

// Another comment.
print "Hello world !" // Another comment
          

Unlike the example given for '#' this example is syntactically correct and will not produce an error.

See also

#, rem


Name

@ — synonymous to at

Synopsis

clear screen
…
print @(a,b)

Description

As '@' is simply a synonym for at, please see at for further information.

See also

at


Name

: — separate commands from each other

Synopsis

print "Hello ":print "World"

Description

The colon (':') separates multiple commands on a single line.

The colon and the newline-character have mostly the same effect, only that the latter, well, starts a new line too. The only other difference is their effect within the (so-called) short if, which is an if-statement without the keyword then. Please see the entry for if for more details.

Example

if (a<10) print "Hello ":print "World !"
          

This example demonstrates the difference between colon and newline as described above.

See also

if


Name

; — suppress the implicit newline after a print-statement

Synopsis

print "foo",bar;

Description

The semicolon (';') may only appear at the last position within a print-statement. It suppresses the implicit newline, which yabasic normally adds after each print-statement.

Put another way: Normally the output of each print-statement appears on a line by itself. If you rather want the output of many print-statements to appear on a single line, you should end the print-statement with a semicolon.

Example

print "Hello ";:print "World !"
          

This example prints Hello World ! in a single line.

See also

print


Name

** or ^ — raise its first argument to the power of its second

Synopsis

print 2**b
print 3^4

Description

** (or ^, which is an exact synonym), is the arithmetic operator of exponentiation; it requires one number to its left and a second one to its right; ** then raises the first argument to the power of the second and returns the result. The result will only be computed if it yields a real number (as opposed to a complex number); this means, that the power can not be computed, if the first argument is negative and the second one is fractional. On the other hand, the second argument can be fractional, if the first one ist positive; this means, that ** may be used to compute arbitrary roots: e.g. x**0.5 computes the square root of x.

Example

print 2**0.5
          

See also

sqrt

Chapter 8. A few example programs

A very simple program

The program below is a very simple program:

repeat
  input "Please enter the first number, to add " a
  input "Please enter the second number, to add " b
  print a+b
until a=0 and b=0

This program requests two numbers, which it than adds. The process is repeated until you enter zero (or nothing) twice.

Graphics with bitmaps

yabasic allows to retrieve and put back rectangular regions of the screen with simple commands:

open window 200,200

rem prepare picture of a star
dim p(3,2)
for off=0 to 90 step 30
  for a=0 to 2
    phi = (off + 120*a)*2*pi/360
    p(a,0) = 50 + 20*cos(phi)
    p(a,1) = 50 + 20*sin(phi)
  next a
  fill triangle p(0,0),p(0,1),p(1,0),p(1,1),p(2,0),p(2,1)
next off

star$ = getbit$(30,30,80,80)
clear window

for a=0 to 200 step 10
  line a,0 to a,200:line 0,a to 200,a: rem draw some pattern on the screen
next a

for a=10 to 150 step 5
  saved$=getbit$(a,80,a+40,120): rem save old content of window
  putbit star$ to a,80,"t": rem put star at new location
  pause 0.5
  putbit saved$ to a,80: rem restore old window content
next a

This program moves moves the picture of a star across the graphics window. The first part of the program draws such a star and then retrieves the bitmap with getbit$(). Yabasic stores bitmaps within ordinary strings and so the star-bitmap can simply be stored within the variable star$.

Once the program has prepared the bitmap-string, it puts it back into the window with the putbit-command and various locations. Each time before the star-bitmap is put into the window, the prior content is saved within the variable saved$ and restored later.

A menu to choose from

This example program presents a menu (e.g. a predefined set of 3 choices) and lets the user choose one of them. The menu is similar (but simpler) to the one employed in the demo of yabasic

//  Initialize menu
restore menudata
read menusize:dim menutext$(menusize)
for a=1 to menusize:read menutext$(a):next a

ysel=1
clear screen
blank$ = "                      "
hash$ = "########################################"
print colour("cyan","magenta") at(7,2) hash$
print colour("cyan","magenta") at(7,3) hash$
print colour("cyan","magenta") at(7,4) hash$
print colour("yellow","blue") at(8,3) " This is a simple menu to choose from "

for a=1 to menusize
  if (a=menusize) then yoff=1:else yoff=0:fi
  if (a=ysel) then
    print colour("blue","green") at(5,7+yoff+a) menutext$(a);
  else
    print at(5,7+yoff+a) menutext$(a);
  endif
next a
print at(3,15) "Select with cursor keys UP or DOWN (or letters u and d),"
print at(3,16) "Press RETURN or SPACE to choose, ESC to quit."

do

  k$=inkey$

  yalt=ysel

  switch k$
  case "up":case "u":
    if (ysel=1) then ysel=menusize else ysel=ysel-1 fi
    redraw()
    break
  case "down":case "d":
    if (ysel=menusize) then ysel=1 else ysel=ysel+1 fi
    redraw()
    break
  case " ":case "enter":case "right":
    if (ysel=menusize) end_it()
    print at(3,18) "You have chosen: " + menutext$(ysel) + blank$
    sleep 1
    print at(3,18) blank$ + blank$
    break
  case "esc":
    end_it()
  default:
    print at(3,18) "Invalid key: " + k$ + blank$
    sleep 1
    print at(3,18) blank$ + blank$
  end switch
loop 

//  redraw line
sub redraw()
  local yoff
  if (yalt=menusize) then yoff=1:else yoff=0:fi	
  print at(5,7+yalt+yoff) menutext$(yalt);
  if (ysel=menusize) then yoff=1:else yoff=0:fi
  print colour("blue","green") at(5,7+ysel+yoff) menutext$(ysel);
  return
end sub

// terminate program
sub end_it()
  print at(3,18) "Bye ..."
  sleep 1
  exit
end sub

//  Data section ...
label menudata
//  Data for main menu: Number and text of entries in main menu
data 4
data "   First Item            "
data "   Item number two       "
data "   Last Item             "
data "   None of the above     "

Some interesting aspects from top to bottom:

  • The text of the various menu-items is initialized at the top of the program; the needed text-strings are kept in data-lines at the end of the program.

  • User-input is aquired with the inkey$-function.

  • A switch-statement is employed to process the input; several keys (e.g. right and enter) are handled in the same case-clause.

  • Two subroutines redraw() and end_it() handle common work, that needs to be done at multiple places in the program.

Chapter 9. The Copyright of yabasic

yabasic may be copied under the terms of the MIT License, which is distributed with yabasic in the file LICENSE.

The MIT License grants extensive rights as long as you keep the copyright notice present in most files untouched. Here is a list of things that are possible under the terms of the MIT License:

  • Put yabasic on your own homepage or CD and even charge for the service of distributing yabasic.

  • Write your own yabasic-programs, pack your program and yabasic into a package and sell the whole thing.

  • Modify yabasic and add or remove features, sell the modified version without adding the sources.