sub isleap {
    my ($year) = @_;
    return 1 if (( $year % 400 ) == 0 ); # 400's are leap
    return 0 if (( $year % 100 ) == 0 ); # Other centuries are not
    return 1 if (( $year % 4 ) == 0 ); # All other 4's are leap
    return 0; # Everything else is not
}