programming-for-dummies

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Creating and Using Subprograms
Figure 6-1:
Every large
program is
made up of
smaller
subprograms
that
act as
building
blocks.
A program can consist of one
massive chunk of code.
Subprograms divide a large program
into smaller pieces to make the
large program easier to create and
modify.
If you wanted to write a horse race prediction program, you wouldn’t have
to write the whole thing from scratch. You could copy the subprograms from
another program and reuse them in your new project, as shown in Figure 6-2.
By reusing subprograms, you can create more complicated programs faster
than before. After programmers create enough useful subprograms, they can
store these subprograms in a “library” that they and other programmers can
use in the future.
Creating and Using Subprograms
A subprogram essentially yanks out two or more commands from your main
program and stores them in another part of your main program or in a separate
file, as shown in Figure 6-3.
The reasons for isolating commands in a subprogram (and out of your main
program) are to
✦ Keep your main program smaller and thus easier to read and modify.
✦ Isolate related commands in a subprogram that can be reused.
✦ Make programming simpler and faster by just reusing subprograms
from other projects.