Other posters have already provided fine solutions so I won't go there but, in general, your code should always include:

use strict;
use warnings;
use diagnostics; # not strictly necessary but really nice
[download]

The other posters did hint at that but I wanted to be more explicit.

Also, in the future it would be especially cool if you would clearly flag homework in the header line.

Hope this helps!

(update: minor clarification mod)