Commodore VIC-20 - Page 111

Chapter 3: Programming the VIC 20 Computer 97
Start of program - =r:
: }
+}~
I Repeated routine
t::J
T
etc.
To solve this problem, you could separate out the repeated statements
and branch to them. This group
of statements is referred to as a subroutine.
But a problem arises. Branching from your program to the subroutine
is simple enough, since the subroutine starts at a given line number. How-
ever, where do you branch back to
at the end of the subroutine? You could
execute a GOTO statement whenever you wish to branch to a subroutine.
Arbitrarily selected
line numbers
Start of
program- 10
Subroutine
-start
__ 2000
--- /..
etc.
100 GOTO 2000 - - - - " .~
110 / /1
/ I,
,/' / I
,," / I
/ 1 /
".I' / /
190 GOTO 200(} / 1 /
200 /1 /
I /
1 /
1 ,
1 /
• I /
250 GOTO 2000' /
260 I
,
/
/
2150
_end
-... ,
\
.... -...... ,
;' '\)
" '1
, "'--,,)/1
;" __ '" 'I
I /I
\ /1
'--" I
I
/
/
Return ","
where?
--
480 GOTO 2000
500