快速格式化错误 - PHP

 if (isset($_GET['z'])) {
 $file = $file ."-" ($_GET['z'];
 }

Can someone tell me what is wrong with my formatting?

Thanks

 if (isset($_GET['z'])) {
      $file = $file . "-" . ($_GET['z']);
 }

you're missing one dot and one )

better one is

 if (isset($_GET['z'])) {
      $file .= "-" . $_GET['z'];
 }