Functions

The Little Engine That Could

• A Perl "function", like a lot of other stuff in computers, is a piece of code that:
• Takes something in.
• Processes it.
• Spits something out.
• Functions are sometimes described as "engines" or "little black boxes" or "itsy bitsy oopie whoopies" (well, not really that last one.)
  
• Functions simplify programming, becasue they encapsulate frequently used tasks.
  
• 2 kinds of functions: Built-in and User Defined
• Built-in: Comes as part of the Perl language (or an extension.)
• User Defined: Well, um, defined by the user (programmer.)  Also called "subroutines"
  
• Built-in Functions
• We've already used one very frequently: print
• There are hundreds, which means that Perl has already done a lot of work for you.
• User Defined
• Example:

          #!perl

          $i = 0;
          $n = 5;

          while ($i < 10) {
            print "I am about to call my subroutine...\n";
            &goofy;
            print "Called it!\n";
            $i++;
          }

          print "The value of variable n is $n\n";
          print "BYE!\n";

          sub goofy {
            print "Hi, I'm goofy.\n";
            $n += 5;
          }

A Useful Built-in (or 2, or 3...)

• Well, actually several useful built-ins.
• How many built-ins are in the following program?
  

     #!perl

     @dogs = qw(Baxter Opie Chaico Lassie Rover);
     $i = 0;

     while ($i<20) {
        $random_array_index = int(rand(scalar(@dogs)));
        print "I pick $dogs[$random_array_index]\n";
        $i++;
     }

• You will need the int(rand blah blah thingy for Project 1