checkAnswer.swift

    func checkAnswer() {
        if typeTextField.text == String(questionNumber) {
            let controller = UIAlertController(title: "答對了", message: "正確答案是\(questionNumber)", preferredStyle: .alert)
            let action = UIAlertAction(title: "Re-Play", style: .default) { (_) in
                self.playAgain()
            }
            controller.addAction(action)
            present(controller, animated: true, completion: nil)
        } else if typeTextField.text! > String(questionNumber) {
            if typeTextField.text! >= String(upperBound) {
                let controller = UIAlertController(title: "數字太大囉！", message: "請輸入範圍內的數字", preferredStyle: .alert)
                let action = UIAlertAction(title: "了解", style: .default) { (_) in
                    self.typeTextField.text = ""
                }
                controller.addAction(action)
                present(controller, animated: true, completion: nil)
            } else {
                chanceNumber -= 1
                upperBound = Int(typeTextField.text!)!
                chanceLabel.text = "你有\(chanceNumber)次機會！"
                rangeLabel.text = "範圍 \(lowerBound) ~ \(upperBound)"
                typeTextField.text = ""
            }
        } else if typeTextField.text! < String(questionNumber) {
            if typeTextField.text! <= String(lowerBound) {
                let controller = UIAlertController(title: "數字太小囉！", message: "請輸入範圍內的數字", preferredStyle: .alert)
                let action = UIAlertAction(title: "了解", style: .default) { (_) in
                    self.typeTextField.text = ""
                }
                controller.addAction(action)
                present(controller, animated: true, completion: nil)
            } else {
                chanceNumber -= 1
                lowerBound = Int(typeTextField.text!)!
                chanceLabel.text = "你有\(chanceNumber)次機會！"
                rangeLabel.text = "範圍 \(lowerBound) ~ \(upperBound)"
                typeTextField.text = ""
            }
        }
    }