programming-for-dummies

158
Defining the Scope of a Variable
Program
File 1 File 2
Figure 2-7:
Subprogram
variables
restrict
access only
to code
stored in
that
particular
subprogram.
X : integer
Y : string
File 3 File 4
Passing data among subprograms
If one subprogram needs to use data stored in another subprogram, what’s
the solution? The easiest (and most dangerous) solution is to let multiple
subprograms access that variable as a global or module variable.
The better solution is to isolate that variable as a subprogram variable and
then share or pass that data to another subprogram. This means you have to
declare two subprograms variables, one in each subprogram. Although cumbersome
(now you know why programs create global or module variables
instead), passing data from one variable to another, dubbed parameter passing,
helps keeps the data isolated in only the subprograms that actually need
to use that data, as shown in Figure 2-8.