Adding Days to a Date with PHP

Question

I am trying to add a certain amount of days to a set date in PHP. However, all of the code I use is not working. Here is the code I am currently experiencing problems with:<

Answer 1

For the sake of completeness, here's how you do it with DateTime():

$datetime = new DateTime("2013-12-01");
$datetime->add(new DateInterval('P7D'));
echo $datetime->format('Y-m-d');

or

$datetime = new DateTime("2013-12-01");
$datetime->modify('+7 days');
echo $datetime->format('Y-m-d');