php - how to add 7 days to a formatted date -

i need able add 7 date formatted date.

i have variable:

$holiday has value of wednesday 1st of january (for example); 

i tryng add 7 days result output 8th of january fails, code use follows

if (strpos($holiday,'1st') && strpos($holiday,'january') == true) {$result = date("l js \of f", strtotime( $holiday. "+ 7 day" ));} 

no errors in php log

so if examples wednesday 1st of january format.

like [day] [daynum] [of] [month]

then can do:

 $date ='wednesday 1st of january';  $arr = explode(' ',$date);  $arr[1]=(int)$arr[1];//we cast `1st` int becomes `1`  unset($arr[2],$arr[0]);//we ignore `of` , `day`  $datenew = implode(' ',$arr);  $d = datetime::createfromformat('j f',$datenew);  print $d->format('y-m-d');//2017-01-01  print $d->modify('+7 days')->format('y-m-d');//2017-01-08