programming-for-dummies

134
Dividing a Program into Subprograms
Subprogram
Figure 1-5:
Storing subprograms
in
separate
files can
make it easy
to read and
modify one
part of a
large
program
without
having to
see any
other part of
that same
program.
Main program
Math commands
Math commands
Saving commands
Saving commands
Printing commands
Printing commands
Printing commands
The more commands you
cram into a program, the
larger the program gets.
Main program
Run math program
Run saving program
Run printing program
By dividing a large
program into smaller
subprograms and storing
those subprograms in
separate files, you can
dramatically shrink the size
of your main program.
Math commands
Math commands
Subprogram
Saving commands
Saving commands
Subprogram
Printing commands
Printing commands
Printing commands
By storing subprograms in separate files, you can write a program with multiple
programming languages. That way you can write your main program in
BASIC and then write subprograms in C or Java. By doing this, you don’t
have to limit yourself to the strengths and weaknesses of a single programming
language. Instead, you can take advantage of the strengths of each programming
language.
If you’re writing a hard disk diagnostic program, you could write the whole
thing in C because C is great for accessing the hardware of a computer.
However, you may find that C is too clumsy for printing reports or displaying
information on-screen. In that case, what are your choices? You can
✦ Use C to write the whole program. This is great for accessing computer
hardware but hard for writing the rest of the program, like the user
interface.
✦ Use an easier language, like BASIC, to write the whole program. This
is great for writing every part of the program except the part needed to
access the computer hardware.
✦ Use a mix of two or more programming languages. Use BASIC to write
most of the program and then use C to write a subprogram to access the
computer hardware.