This function returns number of days in a month

days-in-a-month.php

<?php

function daysInMonth($month) 
{
    $days = 0;
  
    switch ($month) {
        case 1:
            $days = 31;
            break;
        case 2:
            $days = 28;
            break;
        case 3:
            $days = 31;
            break;
        case 4:
            $days = 30;
            break;
        case 5:
            $days = 31;
            break;
        case 6:
            $days = 30;
            break;
        case 7:
            $days = 31;
            break;
        case 8:
            $days = 31;
            break;
        case 9:
            $days = 30;
            break;
        case 10:
            $days = 31;
            break;
        case 11:
            $days = 30;
            break;
        case 12:
            $days = 31;
            break;

        return $days;        
    }
}