How to take dates between two dates in php?

   $task_to_do = array();
   echo "
";
   $s = strtotime("START_DATE");
   $d = strtotime("END_DATE");
   $dif = 86400;
   $i=$s;
   $x=0;
   while ($i <= $d) {
      $dat = date("Y-m-d 00:00:00",$i);
      $t_s = date("Y-m-d 00:00:00",strtotime($dat));
      $t_e = date("Y-m-d 23:59:59",strtotime($dat));
      $task_to_do[$x]["start_date"] = $t_s;
      $task_to_do[$x]["end_date"] = $t_e;
      $i = $i+$dif;
      $x++;
   }
   echo "
";
   print_r($task_to_do);