Help changing code HELP!!!!!!!!!!!!!!!!!

Hey I need your help I want to change a part of the config.php file in my script which is $allow = "1"; // to allow comments 1 = yes 0 = no I'm trying to change it to $allow = "0"; using a other file I have this code but i get errors <? require("config.php"); $changeallow = substr_replace($allow, '0', 0); if ($configallow=="yes") { $data = "$allow = /"0/";"; $fp = fopen("config.php",'a'); $fw = fwrite($fp,$data); fclose($fp); } ?> If you have another code i could use please help me out!!!!!!!!!!!!!!!!!!! Thanks