In the only lecture i had about algorithms the professor told us: "Shure, you can cheat but then you need to explain it to me..." ;-)

#!/usr/bin/perl

use strict;
use warnings;

my ( $c, $f ) = ( 10, 1 );

$f *= $c--  while  $c > 0 ;

print $f;

__END__

karl@host ~
$ ./factorial.pl
3628800
[download]

Wolfram Alpha

Regards, Karl