Atari 800 Basic Reference Manual

ON/GOSUB/
RETURN
ONIGOTO
POP
20 Program Stat emen ts
Format:
ON aexp { GOTO} lineno [ ,lineno .. .]
GO SUB
Examples: 100 ON X GOTO 200, 300, 400
100
ON A GOSUB 1000, 2000
100 ON
SQR(X) GOTO 30, 10, 100
Note: GOSUB and GOTO may not be abbreviated.
These two statements are also conditional branch statements like the IF/THEN
statement . However, these two are more powerful. The aexp must evaluate to a
positive number which is then rounded to the nearest positive integer (whole
number) value up to 255. If the resulting number is 1, then program control
passes to the first lineno in the list following the GOSUB or GOTO. If the
resulting number is 2, program control passes to the second lineno in the list,
and so on. If the resulting number is 0 or is greater than the number of linenos
in the list, the conditions are not met and program control passes to the next
statement which may or may not be located on the sa me line. With ON /GOSUB,
the selected subroutine is executed and then control passes to the next state-
ment.
The following routine demonstrates the ON/GOTO statement:
1 a :=<=r.: + 1
:C.'€1 Ot-.1 :=< GOTO 100 .. 200 .. 30f1 .. 400} 500
313 IF :-:::>5 Tli'H~ PRHH "CIX1PLETE. II : HID
413 GOTO 10
50 END
100 PRHH "t·IDL·J L·JO~~f:::WG AT LH~E 100'': GOTO
10
200 PF.:IrH
"t · [I~J
~·JO~:K I ~-~G AT LH~E 200" = GOTO
Hi
3tl)
F'RHH
"t·KIL·J
L ·J OF.:K I t · ~G AT
LWE
300" : GOTO
10
40J)
PF.:ItH
"t·[ll·J
l ·JORK I t · ~G AT LH~E
400
11
:GOTO
10
50t1 PF.:HH "t · ~O~·J l· JOF. :K IHG AT Lir~E 501-3" : GOTO
w
Figure 4-9 ON / GOTO Program Listing
When the program is executed , it looks like the following:
t·~Ol·J ~·JOF.:KH~ AT LmE 100
t·~C~·l L·lO~:t::: WG AT LINE 200
r~Ql.l ~·lORK n~,; AT LI t-~E 300
t·mL·l l·lORK Hf.~ AT L It-~E 40(1
t·mL·J L· JOF.:K I t·~ ~ AT L I t·~E 500
COt · 1PLETE .
Figure 4-10 ON / GOTO Program Execution
Format: POP
Example: 1000 POP

Atari 800 Specifications

General

Processor	MOS Technology 6502
Processor Speed	1.79 MHz
ROM	10 KB
Graphics	ANTIC and GTIA chips
Release Year	1979
Display Resolution	up to 320 x 192
Colors	128 colors
Sound	4 channels
Storage	Cartridge, cassette, floppy disk
Ports	Cartridge, serial, monitor
Operating System	Atari OS