（一）加法计算器（第一个iOS APP）

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var textOne: UITextField!

    @IBOutlet weak var textTwo: UITextField!

    @IBOutlet weak var textResult: UILabel!

    @IBAction func calculate() {

        var num1 = self.textOne.text.toInt()//从UITextField读取int

        var num2 = self.textTwo.text.toInt()

        if (self.textOne.text.isEmpty){

            num1 = 0

        }

        if (!self.textTwo.hasText()){

            num2 = 0

        }

        var resultNum = num1! + num2!//加！号?

        //两种从int转string的方法

        var resultString = String.convertFromStringInterpolationSegment(resultNum)

        var resultString2 = "\(resultNum)"

        self.textResult.text = resultString2 //UILabel赋值

        self.textOne.endEditing(true)

        self.textTwo.endEditing(true)

    }

    override func viewDidLoad() {

        super.viewDidLoad()

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

    }

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

        // Dispose of any resources that can be recreated.

    }

}