- var_dump: documentation ( source)
- ctype_digit: documentation ( source)
- is_numeric: documentation ( source)
- mktime: documentation ( source)
- date: documentation ( source)
<?php
$day = '01';
var_dump(is_numeric($day));
var_dump(ctype_digit($day));
$a = mktime(0, 0, 0, date('m'), date('d') + $day, date('Y'));
var_dump($a);