Commodore Plus 4 - Control Statements and Loops; CHAPTER 7 Using Graphics and Color

CONTROL
STATEMENTS
AND
LOOPS
n
~
It would be pretty boring if your computer could only execute program
lines in order. The computer could only star! at the beginning and go
through each step in order until the end of the program. This would
lead lo very long programs; if you wanted to do the same thing twice
(like PRINT "HELLO"), you would have lo duplicate the program lines.
With a small example like PRINTing HELLO, this doesn't make a lot of
difference, but it could become difficult in larger programs. This is why
computers have control statements. Control statements tell the com
puter to ignore the normal order of the program lines, and go to another
line regardless of the sequence. The Plus/4 has several varieties of
control statements, unconditional (like GOTO) which always transfer
control; counting statements (like FOR/NEXT} which transfer control
a specified number of times; and, for you structured programming
fans out there, DO/LOOP.
Statement Name: GOTO
Format.GOTO line #
GOTO tells your computer to immediately go from the current line in
your program to the line number specified in the GOTO statement.
For example, if line 20 reads GOTO 40. your Plus/4 would jump to
line 40, skipping any statements between 20 and 40.
Example using GOTO statement in a program.
TYPE:
10 PRINT "A PENNY SAVED IS BETTER THAN NOTHING"
20 GOTO 10
The computer responds by printing the message in line 10 again and
again, until you press the STOP key, like this:
A PENNY SAVED IS BETTER THAN NOTHING
A PENNY SAVED IS BETTER THAN NOTHING
A PENNY SAVED IS BETTER THAN NOTHING
~
BREAK IN 10
READY.
If you press the
STOP key
This print statement will continue 'forever1. Every time your Plus/4 gets
to the GOTO in line 20 it goes back to line 10. This is called an INFINITE
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