The same three numbers,
10,20,
and 30, are displayed, but A,
B,
and C are
variables, not constants. By changing the values assigned to
A,
B,
and
C,
Vou
can
change the values printed
out
by the PRINT
statement
Here
is
an
example:
A=-4B=10'C=4E2PRINT
A,B,C
-4
10
400
Variables appear
in
just
about every statement of a
computer
program.
Variable
Name
A variable
is
identified by a name.
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. 1n
the illustration below, the
cu
rrent
va
lue of A
is
14; for B it
is
15; and for C it
is
O.
Variable
Location
Name
Contents
A
14
B 15
C
0
If
we
change A to
-1
using the immediate mode statement:
A
=-1
then our illustration must change
as
follows:
Variable
Name
A
B
C
Location
Contents
-1
15
o
This
is
a good
way
of looking at variables because it
is,
in
fa
ct
the
way
they
are handled by the
PET.
A variable name represents
an
address
in
PET
memory; and
at
that memory location
is
the current value of the variable. The
important
point
to
note
is
that
variable names - which are names that pro-
grammers make
up
- are arbitrary; they have
no
innate relationship to the
value that the variables represent.
59
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