按＆＃34; q＆＃34;退出程序

Question

当我按q时，我收到错误。我知道什么是错的，但我不知道我会怎么做。在编程的开始，感谢已经

@IBOutlet var HS: UILabel!
@IBOutlet var S: UILabel!

override func viewDidLoad()
{
    super.viewDidLoad()

    let HighscoreDefault = UserDefaults.standard
    let ScoreDefault = UserDefaults.standard
    print("Hi")
    if HighscoreDefault.value(forKey: "Highscore") != nil
    {
        let Highscore = HighscoreDefault.value(forKey: "Highscore") as! Int
        let Score = ScoreDefault.value(forKey: "Score") as! Int
        print(Highscore)
        print(Score)

        S.text = NSString(format: "Score : %i", Score as CVarArg) as String
        HS.text = NSString(format: "Highcore : %i", Highscore as CVarArg) as String
    }