ch03.022_best

Perl Best Practices the source code

##############################################################################
##   Code fragment (Recommended) from Chapter 3 of "Perl Best Practices"    ##
##     Copyright (c) O'Reilly & Associates, 2005. All Rights Reserved.      ##
##  See: http://www.oreilly.com/pub/a/oreilly/ask_tim/2001/codepolicy.html  ##
##############################################################################


# Standard modules...
use strict;
use warnings;
use IO::Prompt;
use Carp;
use English qw( -no_match_vars );
use Data::Alias;
use Readonly;

Readonly my $MAX_FACT => 100;


# Initialize table of factorials
my @factorial = (1);
for my $n (1..$MAX_FACT) {
    $factorial[$n] = $n * $factorial[$n-1];
}
 
# Check availability and look up in table 
sub factorial {
    my ($n) = @_;
 
    croak "Can't compute factorial($n)" 
        if $n < 0 || $n > $MAX_FACT;
 
    return $factorial[$n]; 
}

for my $n (1,2,5,10,100) {
    print "$n! = ", factorial($n), "\n";
}