Commodore Plus 4 - Page 87

SUBROUTINES lf y°u have something in your program that has to be repeated in more
than one place in your program, you have two choices: you can have
duplicate routines, or you can create a subroutine. A subroutine is a
section of your program that can be used from anywhere else in your
program When the subroutine is finished, the program automatically
continues at the statement just after where the subroutine was called.
Statement Name- GOSUB/RETURN
Format:GOSUBIine #
The GOSUB statement is used to call a subroutine. Like the GOTO
statement, control is transferred to the line number specified in the
statement However, unlike the GOTO, the Plus/4 remembers where
the GOSUB is located. When a RETURN is next encountered, control
returns to just after the GOSUB statement.
Example
5T = 0:FORJ = 1 TO 99
10 PRINT "GIVE ME A NUMBER FROM 1 TO 10"
20 INPUT N
30IFN- 1 THEN GOSUB 100:GOTO 20
40IFN 10 THEN GOSUB 100:GOTO 20
50T = T + N
60 NEXTJ
70 PRINT "THE TOTAL IS"J
80 END
100 PRINT "THAT NUMBER IS OUT OF RANGE"
105 PRINT "PLEASE TYPE A NUMBER BETWEEN 1 AND 10
110 RETURN
If a RETURN is encountered when there are no active GOSUBs, you
get a RETURN WITHOUT GOSUB ERROR You should be careful that
the computer never gets into one of your subroutines except by GOTO.
One method is to group the GOSUB and GOTO statements together,
protected from normal program execution by an END statement.
Statement Name REM
Format REM message
The REM statement is used to comment (or REMark) on your pro
grams. The REM statement is not executed as part of the program; it is
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