未定义索引

namespace app\index\controller;
use think\Db;

class Search extends Common
{
	public function  在 dex(){
		$input =  输入 ();

		$this->assign([
			'keyword' => htmlspecialchars($input['key']),
			'cid' => isset($input['cid']) ? htmlspecialchars($input['cid']) : 0
		]);
		return $this->fetch();
	}
}
?>