programming-for-dummies

216
Creating and Using Subprograms
Creating a subprogram
Every subprogram consists of a unique name and one or more commands.
You can name a subprogram anything although it’s usually best to give a
subprogram a descriptive name. So if you create a subprogram to convert
yards into meters, you might name your subprogram Yards2Meters or
MetricConverter.
A descriptive name for a subprogram can help you identify the purpose of
that subprogram.
After you define a name for your subprogram, you can fill it up with one or
more commands that tell that subprogram what to do. So if you wanted to
write a subprogram that prints your name on-screen, your main subprogram
might look like this:
SUB PrintMyName
FOR I = 1 TO 5
PRINT “John Smith”
NEXT I
END SUB
The preceding BASIC language example defines the beginning of a subprogram
by using the SUB keyword followed by the subprogram’s name,
PrintMyName. The end of the subprogram is defined by the END SUB
keywords.
Not every language defines subprograms with keywords. In the curly bracket
language family, the main program is called main and every subprogram is
just given its own name, such as
print_my_name ()
{
for i = 1; i < 5; i++)
{
printf (“John Smith”);
}
}
Instead of using the term subprogram, the curly bracket languages use the
term function.
You can store subprograms in the same file as the main program or in a separate
file. If you store a subprogram in the same file as the main program,
you can place the subprogram at the beginning or end of the file, as shown
in Figure 6-4.