//for in

        let numberList = [, , , , ]

        //获取第一个元素 !拆包

        print(numberList.first!)//1

        //获取最后一个元素

        print(numberList.last!)//5

        //获取元素下标,和对应的元素

        for num in numberList.enumerated() {

            print("\(num.offset)\(num.element)")

        }

        //元素倒序

        for (index, item) in numberList.enumerated().reversed() {

            print("\(index)\(item)")

        }

        //过滤元素(filter)

        for (index, item) in numberList.enumerated().filter({ (index, item) in index >  && index <  }) {

            print("\(index):\(item)")

        }

        for(index,item) in numberList.enumerated().filter({ (i,g) -> Bool in i > }){

            print("\(index):\(item)")

        }

 //if

        let time =

        if time <   {

            print("继续睡觉")

        }else{

            print("起床")

        }

    }

     //guard 与 if 相似, 当条件为false ,才会执行

    func guardCase(){

        let time =

        guard time ==  else {

            print("出去打球")

            return

        }

        print("下雨了")

    }

 //switch

        let dot = (,)

        switch dot {

        case (,):

            print("原点")

            break

        case (,):

            print("x轴上的点")

            break

        case (,):

            print("y轴上的点")

            break

        default:

            break

        }

        //repeat - while 条件成立会继续执行

        var i =

        repeat {

            i +=

            print(i)

        }while i <

         print(i)

 //while

        var g =

        while g >  {

            g -=

            print(g)

        }

        //g 等于0 的时候回跳出while循环

        print(g)