Commodore Plus 4 - Page 56

44 The BASIC Language
Example: 10 OPEN
SO DO UIITIL STOO
30 GET#8 ,K$
40 IF(ASC(K$)AND137>31 THEN PRINT K$
50 LOOP
Opens communica
tion to the disk
directory file.
Repeats a loop until
the status byte indi
cates an end-of-file
or an error.
Assigns one character
from the disk file
toK$.
Prints noncontrol
characters.
60 CLOSE 8 Closes disk file.
GOSUB line number
Branches the program to a subroutine, which is a group of program lines that
performs a reusable task. You can reuse a subroutine as often as you like just by
calling it with the GOSUB command. Subroutines are particularly useful in
programs that repeat a task.
Subroutines can appear anywhere in the program. They are ended by the
RETURN command, which sends program control back to the main body of the
program. Do not exit subroutines with a GOTO command. The program con
tinues at the line following the GOSUB command.
Parameter: starting line number for subroutine
Example:
10 INPUT "WHAT SHAPE DO YOU WANT TO DRAW"; S$
20 INPUT "DO YOU WANT THE SHAPE TO BE RED, BLUE, OR GREEN"; C$
30 IF S$ <> "CIRCLE" THEN INPUT "HOW MANY SIDES DOES THE SHAPE HAVE"; X
35 IF S$ = "CIRCLE" THEN X = 180
37 IF X = 0 THEN PRINT "ZERO IS NOT ALLOWED. REENTER":GOTO 30
40 GOSUB 80
45 REM AFTER SUBROUTINE, PROGRAM RESUMES AT LINE 50
50 INPUT "WANT TO DRAW ANOTHER SHAPE"; A$
60 IF LEFT$(A$,1) = "N" THEN END: ELSE GOTO 10
70 REM BEGIN SUBROUTINE TO DRAW SHAPE
80 GRAPHIC 1,1
85 REM USE INPUT FROM LINE 20 TO SET COLOR IN LINE 110
90 IF LEFTS(C$,1) = "R" THEN C = 3: GOTO 110
100 IF LEFT$(C$,1) = "B" THEN C = 7: ELSE C = 6
110 COLOR 1,C,3
105 REM USE INPUT FROM LINE 30 TO FIGURE NUMBER OF SIDES OF SHAPE
120 CIRCLE, 160,100,60,50,,,,360/X