``` //生成邀請碼 public function makeCode($userId) { // 密碼字符集，可任意添加你需要的字符 $chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'; // $chars = '0123456789'; $password = ''; for ($i = 0; $i < 5; $i++) { $password .= $chars[mt_rand(0, strlen($chars) - 1)]; } return $password . $userId; } ```