PHP Date Calculation (Substraction...)

For PHP date calculations:

1. Get previous date for a given date
2. Get No. of days between two given dates
3. Get previous Monday's date for a given date

//$date is in its Date format:e.g., 2001-11-30


function PreviousDate($date) {
return date('Y-m-d', strtotime($date . " -1 Day"));
}



//day = date1 - date2
function NoOfDays($date1, $date2) {
$Date_List_a1 = explode ( "-", $date1 );
$Date_List_a2 = explode ( "-", $date2 );
$d1 = mktime ( 0, 0, 0, $Date_List_a1 [1], $Date_List_a1 [2], $Date_List_a1 [0] );
$d2 = mktime ( 0, 0, 0, $Date_List_a2 [1], $Date_List_a2 [2], $Date_List_a2 [0] );
$Days = round ( ($d1 - $d2) / 3600 / 24 );
return $Days;
}


//Get Previous Monday for a Given date
function Get_Previous_Monday_Date($date1) {

$week = date('l',strtotime($date1));
if ($week == "Monday")
return null;
for ($i = -1; $i > -8; $i --){
$date = date('Y-m-d', strtotime($date1 . " $i Day"));
$week = date('l',strtotime($date));
if ($week == "Monday")
return $date;
}
}