Commodore 128D - Page 48

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Now there are two variables, labeled A and B, in the computer's
memory, containing the numbers 300 and 600 respectively. If, later in - -
the program, you want to change the value of a variable, just put 1 i
another assignment statement in the program. Add these lines to the
program above and RUN it again. -
50 A = 900*30/10 UJ
60 B = 95+ 32+ 128
70 GOTO 30 £j
You'll have to press the STOP key to halt the program.
Now LIST the program and trace the steps taken by the computer. I i
First, it assigns the value to the right of the = sign in line 10 to the
letter A. It does the same thing in line 20 for the letter B. Next, it - -
prints the messages in lines 30 and 40 that give you the values of A LJ
and B. Finally, it assigns new values to A and B in lines 50 and 60.
The old values are replaced and cannot be recovered unless the - -
computer executes lines 10 and 20 again. When the computer is * i
sent to line 30 to begin printing the values of A and B again, it prints
the new values calculated in lines 50 and 60. Lines 50 and 60 reas- ^- -
sign the same values to A and B and line 70 sends the computer < i
back to line 30. This is called an endless loop, because lines 30
through 70 are executed over and over again until you press the }
RUN/STOP key to halt the program. Other methods of looping are Lj
discussed later in this and the following two sections.
Strings
A string is a character or group of characters enclosed in quotes. \ \
These characters are stored in the computer's memory as a variable ^
in much the same way numeric variables are stored. You can also
use variable names to represent strings, just as you use them to rep- \ /
resent numbers. When you put the dollar sign ($) after the string vari- '—'
able name, it tells the computer that the name is for a string variable,
and not a numeric variable. \ "1
Type NEW and press RETURN to clear your computer's memory, _
then type in the program below: ) 1
10 A$ = "COMMODORE"
20X = 128 }
30 B$ = " COMPUTER" U
40Y = 1
50 ? "THE "A$;X;B$" IS NUMBER "Y
40 USING C128 MODE-Getting Started in BASIC