#!/usr/bin/perl -w

use strict;
sub keyExists;

# Begin Main
my %hash1 = ();  # Initialize empty hash.  Perhaps unnecessary?
%hash1 = (
    "1", "20",
    "2", "20",
    "4", "19",
    "5", "20",
    "10", "20",
    "6", "18");
my %hash2 = ();  # Initialize empty hash.  Perhaps unnecessary?
%hash2 = (
    "1", "19",
    "2", "20",
    "4", "16",
    "5", "19",
    "6", "20");

foreach my $thisKey (sort keys %hash1) {
	# Check whether key from hash2 returns null to protect from undefined key for hash2
	if (isNull(\%hash2, $thisKey)) {
		print "hash2 contains null value for key: $thisKey", "\n"; 
	}
	else {
		my $result = $hash1{$thisKey} - $hash2{$thisKey};
		print "$thisKey $hash1{$thisKey} minus $hash2{$thisKey} equals $result", "\n";
	}
} # End foreach

exit 0;  # End Main

sub isNull {
	my $hashref = shift;	# Reference to hash
	my $key = shift;	# key to check
	my $rc = 0;
	
	if ($hashref->{$key}) {
		$rc = 0;	# Hash returns non-null value
	}
	else {
		$rc = 1;	# Hash returns Null value
	}
	return $rc;
}  # End sub isNull