gistfile1.pl

my @last_days = (31, undef, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);

sub is_leap_year {
    my $year = shift;

    return 0 if $year % 4;
    return 1 if $year % 100;
    return 0 if $year % 400;
    return 1;
}

sub last_day {
    my ($year, $month) = @_;
    if ($month == 2) {
        if (is_leap_year($year)) {
            return 29;
        } else {
            return 28;
        }
    } else {
        return $last_days[ $month - 1 ];
    }
}

my @days = (
    [ 1900, 2 ],
    [ 2000, 2 ],
    [ 2009, 8 ],
    [ 2009, 9 ],
);
foreach my $set (@days) {
    print "@$set -> ", last_day(@$set), "\n";
}