Handout 7

Overview

• You should have received your homework back from me by email; the next assignment is now on the web page.
• Questions from last time
• Practice (continued)
• Subroutines

Practice continued...

• Write a program that takes a list of words on the command-line and finds the first one alphabetically.
• Hard: write a program that takes a list of words on the command-line and sorts them alphabetically.

Subroutines

• Variables allow you to reuse data (example → example); subroutines allow you to reuse commands (example → example).
• Subroutines have this syntax:

  		sub subroutine-name {
  			list of statements
  		}

• Subroutines can take an argument or return an argument. Taking or returning an argument allows you to separate off the reused commands from the data they operate on.
• When your subroutine takes an argument, you simply pass the argument to the subroutine in the following parentheses just as you would to any built-in function. The subroutine itself has access to any arguments by invoking the shift() command (example → example).
• When shift() is given without an argument in a subroutine, it automatically takes the special array variable @_ as an argument. That special variable is roughly analogous to @ARGV, but at the level of a subroutine: all the arguments given to a subroutine are elements in that arrray. They can be called directly, rather than by using shift() (example).