programming-for-dummies

568
Creating Functions
If you don’t know how many times you need to repeat commands, use a
WHILE loop, which looks like this:
while (condition) {
Command;
Command;
}
If the condition is True, the loop runs at least once. If this condition is
False, the loop doesn’t run. In Python, the WHILE loop looks like this:
while (condition):
Command
Command
Somewhere inside a WHILE loop, you must have a command that can change
the condition from True to False; otherwise, the loop will never end, and
your program will appear to hang or freeze.
Creating Functions
In Perl and Python, every subprogram is a function that can return a value.
The format of a typical Perl function looks like this:
sub functionname {
Commands;
return $value;
}
When you pass parameters to a Perl function, that function can access them
with the foreach keyword and the @_ array, such as
sub functionname {
foreach $variablename (@_) {
Commands;
}
return $value;
}
The foreach $variablename (@_) line stores a list of parameters in the
@_ array. Then the foreach command plucks each item from the @_ array
and temporarily stores it in $variablename.