GFA BASIC Guide (A-E)

A

ABS(x)

Returns the absolute value of a number.

ADD var,n

Increases the value of var by n.

ALERT a,message$,b,button$,var

Creates an alert box where:

a	Defines the alert symbol, 0=none, 1=!, 2=?, 2=stop
message$	Contains the main text, upto 4 lines (each 30 characters) separated by '\|'
button$	Contains the button text, upto 4 strings separated by '\|'
b	Defines the default button, 0 to 3
var	Contains the number of the button selected, 0 to 3 where 3 is both

ARRAYFILL field(),n

Assigns the value n to all elements of an array.

ARRPTR(var)

Returns the address of an array or string descriptor (6 bytes).

ASC(x$)

Returns the ASCII code of the first character in a string.

ATN(x)

Returns the arc tangent of x which is in radians.

B

BASEPAGE: Returns the GFA BASIC basepage.
BGET [#]i,address,n: Reads n bytes from a data channel into memory starting at address.
BIN$(x): Returns a string containing the binary value of x.
BITBLT s%(),d%(),p%(): Raster copying command similar to GET and PUT. s% is the description of the source raster and d% the destination raster. p% contains the co-ordinates of the 2 equally sized rectangles and the copying mode.
BLOAD "filename" [,address] BSAVE "filename",address,length: Load and save memory from and to the disc drive.
BMOVE start,destination,n: Moves n bytes starting at address to another area of memory starting at destination.
BOX x,y,xx,yy: Draws a rectangle with corners at x,y and xx,yy.
BPUT [#]i,address,n: Writes n bytes from memory (starting at address) to data channel i.

C

C:var(arguments): Calls a C program with arguments, e.g. a=C:q%(17,l:0,w:-1).
CALL var CALL var(arguments): Calls a machine code program at address var.
CHAIN "filespec": Loads a program file into the work area and starts it.
CHDIR "directory": Changes the current directory.
CHDRIVE n: Sets the default disk drive.
CIRCLE x,y,r [,phi0,phi1]: Draws a circle centred at x,y with a radius of r. The starting and finishing angles may also be specified as phi0 and phi1.
CLEAR: Clears all variables and fields.
CLEARW n: Clears the contents of the window numbered n.
CLOSE [[#] n]: Close a data channel to the disk drive.
CLOSEW n: Closes the window numbered n.
CLR var [,var ...]: Initializes the specified variables to 0.
CLS [#n]: Clears the screen.
COLOR c: Sets the drawing colour.
CONT: Resumes program execution after a STOP.
COS(x): Returns the cosine of x which is in radians.
CRSCOL CRSLIN: Returns the current cursor line and column.
CVI(x$): Converts a 2-byte string to a 16-bit integer.
CVL(x$): Converts a 4-byte string to a 32-bit integer.
CVS(x$): Converts a 4-byte atari basic string to a number.
CVF(x$): Converts a 6-byte GFA basic string to a number.
CVD(x$): Converts an 8-byte mbasic string to a number.

D

DATA constant [,constant ...]

Creates memory variables that can be read with READ.

DATE$

Returns a date string in the format dd.mm.yyyy.

DEC var

Reduces the value of var by 1.

DEFFILL [col,][style,][pattern] DEFFILL [col,]a$

Defines a fill pattern.

style	0=empty, 1=filled, 2=dots, 3=lines, 4=user defined
pattern	24 dotted patterns and 12 lined can be chosen
a$	A 16 by 16 bit user defined fill pattern

DEFFN name [(varlist)]=EXPRESSION CALLED UP BY: FN name [(expression list)]

Defines a function.

DEFLINE style,width,start,end

Defines the line style.

DEFLIST x

Defines the program listing format. Where x=0, commands are displayed in uppercase and variables in lowercase. Where x<>0 the first letter of each word is capitalised.

DEFMARK [c,][a,][g]

Defines the corner points used when using POLYMARK.

c	The colour register number.
a	Defines the type of mark, where 1=dot, 2=plus, 3=asterisk, 4=square, 5=cross, 6=hash.
g	Defines the size of mark.

DEFMOUSE n DEFMOUSE a$

Selects a pre-defined mouse type or defines a new one. n may be 0 (arrow), 1 (rounded x), 2 (bee), 3 (pointing hand), 4 (open hand), 5 (thin crosswire), 6 (thick crosswire), 7 (bordered crosswire). a$ may contain a 16 by 16 bit pattern plus a mask.

DEFNUM n

Rounds all real numbers to n digits before output. n is of the range 3 to 11.

DEFTEXT [color,][style,][rotation,][size]

Defines the text style used by TEXT.

style	0=normal, 1=bold, 2=light, 4=italic, 8=underlined, 16=bordered. These may be combined.
rotation	Either 0^o (0), 90^o (900), 180^o (1800) or 270^o (2700).
size	4=icon, 6=8 by 8, 13=standard, 32=enlarged.

DFREE(n)

Reports free disk space on drive n.

DIM var(indices) [,var(indices) ...]

Defines an array.

DIM?(field())

Determines the number of elements in an array.

DIR ["filespec" [TO "file"]]

Lists files on a disk.

DIR$(n)

Names the active directory for drive n.

DIV var,n

Divides var by n.

DO ... LOOP

Creates an endless loop, terminated only by EXIT.

DRAW [TO] x,y DRAW x1,y1 TO x2,y2 [TO x3,y3 ...]

Draws points, draw a line from the last plot, or connects a number of points.

E

EDIT: In direct mode it returns you to the editor. Within a program it is equivalent to END.
ELLIPSE x,y,rx,ry [,phi0,phi1]: Draws an ellipse at x,y with a horizontal length of rx and a height of ry. phi0 and phi1 may be used to specify start and finishing angles, in tengths of degrees.
END: Closes all files and terminates program execution.
EOF([#]n): Tests whether the file pointer is at the end of a file.
ERASE field(): Deletes an array.
ERR: Returns the code of a previous error.
ERROR n: Simulates the occurrence of error code n.
EVEN n: Determines if a number is even.
EXEC flag,name,command_line,env_string: Executes a compiled program from disc. flag is either 0 (load and go) or 3 (load only). The environment string env_string may be "".
EXIST("filespec"): Determines whether a file is present, returning -1 (TRUE) if successful, otherwise 0 (FALSE).
EXIT IF condition: Enables a loop to be left if condition is true, irrespective of the loops original condition.
EXP(x): Calculates the value of an exponent.