date to string in php

$s = '06/10/2011 19:00:02';
$date = strtotime($s);
echo date('d/M/Y H:i:s', $date);
The above one is the one of the example of converting a string to date.
echo $s ->format('Y-m-d');
The above one is another method 

<?php
$date = new DateTime('2000-01-01');
echo $date->format('Y-m-d H:i:s');
?>

echo date('Y.m.d H:i:s');