Commodore VIC-20 - Data

by pushing together, or concatenating, two separate strings to form
one longer string. We will describe this further when we discuss i
string variables in general.
Earlier in the chapter, we introduced the concept of a variable. In
this discussion variables are described more thoroughly.
Available is a data item whose value may be changed. The value
is determined by the number assigned to the variable. If you type
the immediate mode statement:
PRINT 10, 20, 30
10 20 30
The VIC will display the same three numbers (as illustrated
above) whenever the PRINT statement is executed; that is
because this PRINT statement used constant data. However, you
can write the immediate mode statement:
A=10: B = 20: C = 3Q: PRINT A, B, C
10 20 30
The same three numbers, 10, 20T 30p are displayed; however. A, j
B, and C are variables, not constants. By changing the values
assigned to A, B, and C, you can change the values printed out by
the PRINT statement. Consider the following example of this:
A- -4: B-45; C-4E2: PRINT AT B, C
-4 45 400
You will notice that variables appear in virtually all computer
programs.
Variables are identified by names. We used A, B, and C as
variable names in the illustrations above. A variable has two parts:
its name and a value. The variable name represents a location at
which the current value is stored. In the following illustration, the
current value of A is 14; for B it is 15; and for C it is 0.
Variable
Name Contents
A 14
B 15
C 0
If we change A to -1 using the immediate mode statement:
A=-1
then the Location Contents, stored under the variable-name AT will
change from 14 to -1.
This is an excellent way of looking at variables because it is, in
5a