Swift - 基本数据类型，及常/变量声明

extension UIFont {
    class func fontName(fontName: String, size fontSize: CGFloat) -> UIFont {
        
        return UIFont(name: fontName, size: fontSize)!
    }
}
class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        self.navigationItem.title = "Swift"
        
        ///1.常量
        let number: Int = 10
        print("the number is \(number)")
        //1.1变量
        var string :String = "hello world!"
        print("\(string.count)个字符")
        //1.2检查字符串是否有特定前缀/后缀：hasPrefix/hasSuffix
        if string.hasPrefix("hello") {
            print("hello首部")
        }
        if string.hasSuffix("!"){
            print("!在尾部")
        }
        //1.3空字符串
        string = "";
        if string.isEmpty {
            print("空字符串")
        }else{
            print("非空字符")
        }
        //1.4 元组
        let myproject = (one:"game",two:12345)
        print("myproject:\(myproject)")
        
        //1.3 获取随机数
        let temp:Int = Int(arc4random()%100) + 1;
        print(temp)
        let temps : Int = Int(arc4random_uniform(100)) + 1;
        print(temps)
        
        /// 创建label
        let label = UILabel.init(frame: CGRect.init(x: 10, y: 15 + TOP_HEIGHT, width: SCREEN_WIDTH - 20, height: 30))
        label.text = "the number is \(number)"
        label.backgroundColor = RED_COLOR;
        label.textColor = GREEN_COLOR
        label.font = UIFont.fontName(fontName: "PingFangSC-Regular", size: 14)
        view.addSubview(label)
        var variableNumber = 42
        variableNumber = 24
        print("the variableNumber is \(variableNumber)")
        
        
        
    }