date format php datetime

PHP
<?php
  // To change the format of an existing date
  $old_date_format = "20/03/1999";
  $new_data_format = date("Y-m-d H:i:s", strtotime($old_date_format));<?php
$date = new DateTime('2000-01-01');
echo $date->format('Y-m-d H:i:s');
?>


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