session_start();
header ( "Content-type: text/html; charset=utf-8" );
if($_SESSION["goodsid"]==""){
    $_SESSION["goodsid"]=$_GET["id"]."@";
}else{
    $array=explode("@",$_SESSION["goodsid"]);
    if(in_array($_GET["id"],$array)){
        $key=array_search($_GET["id"],$array);
        $array[$key]="";
        $_SESSION["goodsid"]=implode("@",$array);
        }else{
        $_SESSION["goodsid"].=$_GET["id"]."@";
        }
}