- sprintf: documentation ( source)
<?php
$month = 5;
$month = sprintf("%02d", $month);
echo $month;
echo "\r\n";
$monthStart = new DateTime();
$monthStart->setDate(2013, $month, 01);
echo $monthStart->format('jS, F Y');
echo "\r\n";
echo $monthStart->getTimestamp();
echo "\r\n";
$monthEnd = new DateTime();
$monthEnd->setDate(2013, $month, 32);
echo $monthEnd->format('jS, F Y');
echo "\r\n";
echo $monthEnd->getTimestamp();
echo "\r\n";