use strict;
use warnings;
use Data::Dumper;
use List::Util qw(min);


my @tests = (
    [qw{ABCGE ABCGE}],
    [qw{ABCGE FGCGB}],
    [qw{ABCGE JHAGT}],
);


foreach my $arry_ref (@tests)
{
    my ($str1,$str2) = @$arry_ref;
    
    # perhaps optional check to use shortest length
    my $len = min (length ($str1), length($str2));
    
    my $c_delta = 0;
    my $i =0;
    
    while ($i < $len)
    {
        $c_delta++ if (substr($str1,$i,1) ne substr($str2,$i,1));       
        $i++;
    }
    
    print "$str1 $str2 $c_delta\n";
}
__END__
ABCGE ABCGE 0
ABCGE FGCGB 3
ABCGE JHAGT 4