convert date php

$time = strtotime('10/16/2003');

$newformat = date('Y-m-d',$time);

echo $newformat;
// 2003-10-16

$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 

$originalDate = "2010-03-21";
$newDate = date("d-m-Y", strtotime($originalDate));