<?php
	$ext = "rar,zip,gif,php";
	$e = explode(',',$ext);
	var_dump($e);
	if(in_array('rar' , $e)){
	    echo"yes";
	}else{
	    echo"no";
	}
?>

array(4) {
  [0]=>
  string(3) "rar"
  [1]=>
  string(3) "zip"
  [2]=>
  string(3) "gif"
  [3]=>
  string(3) "php"
}
yes