Swift 流程控制

概述一.for循环 for－in 实例1： for index in 1...5{ print("\(index)times 5 is \(index * 5)") }结果： 1times 5 is 52times 5 is 103times 5 is 154times 5 is 205times 5 is 251...5表示：［1，5］大

一.for循环

for－in

实例1：

       for index in 1...5{            print("\(index)times 5 is \(index * 5)")        }

结果：

1times 5 is 52times 5 is 103times 5 is 154times 5 is 205times 5 is 25

1...5表示：［1，5］大于等于1且小于等于5

如果括号内不使用index，可以用_代替：

 var a = 5        for _ in 1...5{            a += 1        }        print("\(a)")

结果：

10

遍历数组：

 let nameArr = ["lili","Marry","xiaoming"]        for name in nameArr {            print("Hello,\(name)!")        }       

结果：

Hello,lili!Hello,Marry!Hello,xiaoming!

遍历字典：

  let ageDict = ["lili":9,"Marry":10,"xiaoming":12]        for (name,age) in ageDict {            print("\(name) is \(age)!")        }

结果：

Marry is 10!lili is 9!xiaoming is 12!

由于字典是无序的，所以结果不一定按顺序输出。

二。while循环

语法：

    while condition {        statements    }

举例：

   //唉，举例无能        var a = 10        while a>0 {            a = a-2        }        print(a)

结果：0

原来的do...while循环在此处替换成了repeat...while循环。（不举例了）

三。switch

实例：

        let someCharacter: Character = "z"        switch someCharacter {        case "a":            print("The first letter of the Alphabet")        case "z":            print("The last letter of the Alphabet")        default:            print("Some other character")        }

结果：

The first letter of the Alphabet

＊ 注意：与C和Objective_C不同，3.0的swift中switch语句的case中不再需要使用break跳出switch语句，匹配条件后即跳出Switch语句，同时，switch中的default是必须的。

虽然break在switch中不再是必须的，但是由于switch中的case／default中语句不允许有空语句，此时，我们可以使用break跳出语句。

例如：

    let anotherCharacter: Character = "a"        switch anotherCharacter {        case "a": // InvalID,the case has an empty body        case "A":            print("The letter A")        default:            print("Not the letter A")        }        if let integerValue = possibleIntegerValue {            print("The integer value of \(numberSymbol) is \(integerValue).")        } else {            print("An integer value Could not be found for \(numberSymbol).")        }

case "a":是无效的，这将导致程序报错： 'case' label in a 'switch' should have at least one executable statement。

再看下面这个例子

  let numberSymbol: Character = "三"  // Chinese symbol for the number 3        var possibleIntegerValue: Int?        switch numberSymbol {        case "1","١","一","๑":            possibleIntegerValue = 1        case "2","٢","二","๒":            possibleIntegerValue = 2        case "3","٣","三","๓":            possibleIntegerValue = 3        case "4","٤","四","๔":            possibleIntegerValue = 4        default:            break        }        if let integerValue = possibleIntegerValue {            print("The integer value of \(numberSymbol) is \(integerValue).")        } else {            print("An integer value Could not be found for \(numberSymbol).")        }        // Prints "The integer value of 三 is 3."

此时，default中的可能性很多，我们可能不再需要设置一个possibleIntegerValue的值，此时就可以使用break跳出switch语句。

间隔匹配：

例如：

 let grade = 67        switch grade {        case 0...59:            print("不及格")        case 60...79:            print("及格")        case 80...89:            print("良好")        case 90...100:            print("优秀")        default:            break        }//输出：及格

元祖（Tuples）匹配：

    let somePoint = (1,1)    switch somePoint {    case (0,0):        print("(0,0) is at the origin")    case (_,0):        print("(\(somePoint.0),0) is on the x-axis")    case (0,_):        print("(0,\(somePoint.1)) is on the y-axis")    case (-2...2,-2...2):        print("(\(somePoint.0),\(somePoint.1)) is insIDe the Box")    default:        print("(\(somePoint.0),\(somePoint.1)) is outsIDe of the Box")    }    // Prints "(1,1) is insIDe the Box"

下划线（_）也称为通配符，可以匹配任何可能的值。

值绑定：

    let anotherPoint = (2,0)    switch anotherPoint {    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))")    }    // Prints "on the x-axis with an x value of 2"

where：Switch中还可以使用where来设置附加条件

例如：

    let yetAnotherPoint = (1,-1)    switch yetAnotherPoint {    case let (x,y) where x == y:        print("(\(x),\(y)) is on the line x == y")    case let (x,y) where x == -y:        print("(\(x),\(y)) is on the line x == -y")    case let (x,y):        print("(\(x),\(y)) is just some arbitrary point")    }    // Prints "(1,-1) is on the line x == -y"

控制转移语句：

1.continue；

2.break（不再重复说明）;

3.fallthrough;

4.return.

5.throw。

continue:跳出当前循环，执行下一次循环。

例如：

    let puzzleinput = "great minds think alike"    var puzzleOutput = ""    for character in puzzleinput.characters {        switch character {        case "a","e","i","o","u"," ":            continue        default:            puzzleOutput.append(character)        }    }    print(puzzleOutput)    // Prints "grtmndsthnklk"

fallthrough:条件匹配成功后，继续执行后面的语句。

例如：

    let integerToDescribe = 5    var description = "The number \(integerToDescribe) is"    switch integerToDescribe {    case 2,3,5,7,11,13,17,19:        description += " a prime number,and also"        fallthrough    default:        description += " an integer."    }    print(description)    // Prints "The number 5 is a prime number,and also an integer."

return：跳出整个循环与语句。 总结

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