xCode按钮不会在标签中显示结果

Question

由于某种原因，当我单击计算按钮时，它不会在我创建的名为resultLabel的标签中显示我的结果。开关工作但不是按钮。我是编码的新手，本课的书是针对xCode 6的，我有最新版本的xCode。我检查了我的代码，但似乎无法找出问题，因为我没有错误。谢谢你的帮助。

import UIKit

class ViewController: UIViewController {
// properties for programmatically interacting with UI components
    @IBOutlet weak var switchControl: UISwitch!
    @IBOutlet weak var switchLabel: UILabel!
    @IBOutlet weak var weightTextField: UITextField!
    @IBOutlet weak var heightTextField: UITextField!
    @IBOutlet weak var resultLabel: UILabel!
    var w:Float = 0;
    var h:Float = 0;
    var bmi:Float = 0;

    override func viewDidLoad() {
        super.viewDidLoad()
        // select weightTextField so keypad displays when the view loads
        weightTextField.becomeFirstResponder()

        // Do any additional setup after loading the view, typically from a nib.
    }

    @IBAction func changeSwitchLabel(_ sender: UISwitch) {


        if (sender.isOn == true) {
            switchLabel.text = "Eng"
        }
        else{
            switchLabel.text = "Met"
        }
    }

    @IBAction func calculateBMI(_ sender: Any) {
      if switchControl.isOn == true
      {
            let strW:NSString = weightTextField.text! as String as NSString
            w = strW.floatValue

            let strH:NSString = heightTextField.text! as String as NSString
            h = strH.floatValue

            bmi = (w * 702) / (h * h)
           var str = ""

            switch (bmi)
            {
            case 0...18.5:
                str = NSString(format: "Your BMI is %.2f ", bmi, ". You are Underweight") as String
            case 18.5...24.9:
                str = NSString(format: "Your BMI is %.2f ", bmi, ". You are Normal") as String
            case 25...29.9:
                str = NSString(format: "Your BMI is %.2f ", bmi, ". You are Overweight" ) as String
            default:
                str = NSString(format: "Your BMI is %2.f ", bmi, ". You are Obese") as String
            }

         resultLabel.text = str

       }
        else
       {


           let strW:NSString = weightTextField.text! as String as NSString
            w = strW.floatValue

            let strH:NSString = heightTextField.text! as String as NSString
            h = strH.floatValue

            bmi = w / (h * h)
            var str = ""

            switch (bmi)
            {
            case 0...18.5:
                str = NSString(format: "Your BMI is %.2f ", bmi, ". You are Underweight") as String
            case 18.5...24.9:
                str = NSString(format: "Your BMI is %.2f ", bmi, ". You are Normal") as String
            case 25...29.9:
                str = NSString(format: "Your BMI is %.2f ", bmi, ". You are Overweight" ) as String
            default:
                str = NSString(format: "Your BMI is %2.f ", bmi, ". You are Obese") as String
            }

            resultLabel.text = str
       }
    }


}