今天练习代码：

import UIKit

class ViewController: UIViewController {

@IBOutlet weak var op1: UITextField!

@IBOutlet weak var op2: UITextField!

@IBOutlet weak var result: UILabel!

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.

}

@IBAction func add(sender: AnyObject) {

let _op1 = Int(op1.text!)

let _op2 = Int(op2.text!)

let resultValue = _op1! + _op2!

result.text = String(resultValue)

}

}

学到的东西：

toInt() 已经过时，现在的话，需要使用Int(String) 转换

var 与 let 的区别

为什么用var 会有警告，不是很清楚，求大神指点