笔记02 swift 流程控制

//        switch必须要保证能处理所有情况  case、default后面至少要有一条语句 如果不想做任何事，加个break即可，fallthrough是贯穿当前判断
        
        var num = 1
        num = Int(arc4random())
        switch num {
        case 1:
            print("1")
        case 2:
            print("2")
        case 3:
            break
        case 4:
            print("4")
        case 5:
            print("5")
            fallthrough
        case 6:
            print("5 or 6")
            
        default:
            print("other \(num)")
        }
        
        //如果能保证已处理所有情况，也可以不必使用default
        enum Answer { case right, wrong }
        
        let answer = Answer.right
        switch answer {
        case Answer.right:
            print("right")
        case Answer.wrong:
            print("wrong")
        }
        
         // 由于已确定answer是Ansewer类型，因此可以省略Answer
        switch answer {
        case .right:
            print("right")
        case .wrong:
            print("wrong")
        }
        
        //复合条件
       // switch也支持Character、String类型
        let string = "Jack"
        
        switch string {
            case "Jack":
                fallthrough
            case "Rose":
                print("Right person")
            default:
            break
        } // Right person
        
        let character: Character = "a"
        switch character {
        case "a", "A":
            print("The letter A")
        default:
            print("Not the letter A")
        } // The letter A
        
        switch string {
            case "Jack", "Rose":
                print("Right person")
            default:
            break
        } // Right person
        
//        区间匹配
          let count = 62
        switch count {
        case 0:
            print("none")
        case 1..<5:
            print("a few")
        case 5..<12:
            print("several")
        case 12..<100:
            print("dozens of")
        case 100..<1000:
            print("hundreds of")
        default:
            print("many")
        } // dozens of
        
//       元组匹配
        let point = (1, 1)
        switch point {
        case (0, 0):
            print("the origin")
        case (_, 0):
            print("on the x-axis")
        case (0, _):
            print("on the y-axis")
        case (-2...2, -2...2):
            print("inside the box")
        default:
        print("outside of the box") } // inside the box
        //可以使用下划线 _ 忽略某个值
        //关于case匹配问题，属于模式匹配(Pattern Matching)的范畴，以后会再次详细展开讲解
        
        //值绑定
        let point2 = (2, 0)
        switch point2 {
            case (let x, 0):
                print("on the x-axis with an x value of \(x)")
            case (0, let y):
                print("on the y-axis with a y value of \(y)")
            case let (x, y):
                print("somewhere else at (\(x), \(y))")
        } // on the x-axis with an x value of 2
        //必要时let也可以改为var
        
//        where
         let point3 = (1, -1)
        switch point3 {
        case let (x, y) where x == y:
            print("on the line x == y")
        case let (x, y) where x == -y:
            print("on the line x == -y")
        case let (x, y):
            print("(\(x), \(y)) is just some arbitrary point")
        } // on the line x == -y
        
        // 将所有正数加起来
        let numbers = [10, 20, -10, -20, 30, -30]
        var sum = 0
        for num in numbers where num > 0 { // 使用where来过滤num
            sum += num
        }
        print(sum) // 60

//        标签语句
        outer: for i in 1...4 {
            for k in 1...4 {
                if k == 3 {
                    continue outer
                }
                
                if i == 3 {
                    break outer
                }
                print("i == \(i), k == \(k)")
            }
        }