function days_in_month($month, $year) {

    // calculate number of days in a month

    return $month == 2 ? ($year % 4 ? 28 : ($year % 100 ? 29 : ($year % 400 ? 28 : 29))) : (($month - 1) % 7 % 2 ? 30 : 31);

}

echo days_in_month(2,2014);