programming-for-dummies

132
Dividing a Program into Subprograms
Dividing a Program into Subprograms
The smaller the program, the easier it is to write, read, and modify later. So
rather than create a massive program, with related commands organized into
groups, you can divide a large program into smaller pieces, or subprograms.
Subprograms essentially break up a large program into multiple miniature
programs with each miniature program acting like a building block to create
a much larger program, as shown in Figure 1-4. So rather than build a large
program entirely out of keywords, you can build a program out of keywords
and subprograms (which are themselves made up of keywords).
Math subprogram
Math commands
Math commands
Figure 1-4:
Subprograms
create
reusable
building
blocks that
you can use
to make
writing
programs
even easier.
Saving subprogram
Printing subprogram
Subprograms act like bigger
building blocks that make a
large program easier to read
and understand.
Saving commands
Saving commands
Printing commands
Printing commands
Printing commands
The program on the left,
divided into subprograms, is
equivalent to this program
with every command visible.
Think of subprograms as a way to create keywords that aren’t built into the
programming language. For example, the C programming language doesn’t
have any keywords for working with text strings, so programmers have used
C’s existing keywords to create subprograms that can work with text strings.
By using these existing subprograms, other C programmers can manipulate
text strings without writing their own commands.
Using keywords alone to create a program is like trying to build a skyscraper
out of bricks. It’s possible, but it takes a long time to layer enough bricks to
reach the height of a typical 50-story skyscraper.