programming-for-dummies

Retrieving Data from a Variable 151
When storing data in variables, make sure the variable is either empty or
contains data you can afford to lose. Variables can hold only one item at a
time, so storing a new value in a variable wipes out the old value, as shown
in Figure 2-4 and in the following BASIC code:
Salary = 25000
Salary = 17000 + 500
PRINT “This is the value of the Salary variable = “, Salary
Salary = 20000
Stores
20000 in the
Salary variable
20000
Salary
variable
Book II
Chapter 2
Salary = 17000 + 500
17500
Salary
variable
Variables,
Data Types,
and Constants
Figure 2-4:
Assigning a
new value
to a variable
wipes out
the old
value.
Adds 17000 + 500 (17500), erases the old value in
the Salary variable (20000), and stores 17500 in the
Salary variable
PRINT “This is the value of the Salary variable = ”, Salary
This is the value of the Salary variable = 17500
If you store a value in a variable and then immediately store a second value
in that same value, you wipe out the first value in that variable. Obviously,
there’s no point in storing data in a variable only to wipe it out later, so when
you store a value in a variable, you’ll eventually want to use that value again.
(Otherwise, there’s no point in storing that data in the first place.)
Retrieving Data from a Variable
After you store data in a variable, you can treat that variable exactly like a
fixed value. In this first Python language example, the print command just
prints, “This is when I plan on retiring = 65”.
print “This is when I plan on retiring = “, 65