Swift Control Flow控制流

一.For-in

1.  ...

在下面的例子是打印从1到6的数,  1...6  1是开头 6是结尾,开头和结尾都包括在其中。

第一个例子：

for index in 1...6{    print("index = \(index)")}

打印:

index = 1index = 2index = 3index = 4index = 5index = 6

第二个例子：

这个例子相当于普通的for循环。 for(int i = 1;i < 10;i++)

let base = 3let power = 10var answer = 1for _ in 1...power {    answer *= base}print("\(base) to the power of \(power) is \(answer)")

打印：

3 to the power of 10 is 59049

2.数组的遍历

let names = ["Anna", "Alex", "Brian", "Jack"]for name in names {    print("Hello, \(name)!")}

打印：

Hello, Anna!Hello, Alex!Hello, Brian!Hello, Jack!

3.字典的遍历

let numberOfLegs = ["spider": 8, "ant": 6, "cat": 4]for (animalName, legCount) in numberOfLegs {    print("\(animalName)s have \(legCount) legs")}

打印：

ants have 6 legscats have 4 legsspiders have 8 legs

4.字符串的遍历

for character in "Dog!".characters {    print(character)}

打印：

Dog!

二、Repeat-While

先执行循环，知道条件为假就结束，和do-while一样。

repeat {    statements} while condition

三、if

这个没什么好讲的。

var temperatureInFahrenheit = 90if temperatureInFahrenheit <= 32 {    print("It's very cold. Consider wearing a scarf.")} else if temperatureInFahrenheit >= 86 {    print("It's really warm. Don't forget to wear sunscreen.")} else {    print("It's not that cold. Wear a t-shirt.")}

打印：

It's really warm. Don't forget to wear sunscreen.

四、Switch

可以多个条件，可以不要break。

switch some value to consider {case value 1:    respond to value 1case value 2,value 3:    respond to value 2 or 3default:    otherwise, do something else}

例子1：

let someCharacter: Character = "e"switch someCharacter {case "a", "e", "i", "o", "u":    print("\(someCharacter) is a vowel")case "b", "c", "d", "f", "g", "h", "j", "k", "l", "m","n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z":    print("\(someCharacter) is a consonant")default:    print("\(someCharacter) is not a vowel or a consonant")}// prints "e is a vowel"

例子2：

let anotherCharacter: Character = "a"switch anotherCharacter {case "a":    print("The letter a")case "A":    print("The letter A")default:    print("Not the letter A")}// this will report a compile-time error

例子3：

元组的switch - case

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"

例子4：

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"

例子5：where

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"

例子6：Continue

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"

打印的时case之外的字符串

例子7：break

let numberSymbol: Character = "三"  // Simplified Chinese for the number 3var possibleIntegerValue: Int?switch numberSymbol {case "1", "١", "一", "๑":    possibleIntegerValue = 1case "2", "٢", "二", "๒":    possibleIntegerValue = 2case "3", "٣", "三", "๓":    possibleIntegerValue = 3case "4", "٤", "四", "๔":    possibleIntegerValue = 4default:    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."

例子8：fallthrough

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

例子9：#available

检查API的有效性

if #available(platform name version, ..., *) {    statements to execute if the APIs are available} else {    fallback statements to execute if the APIs are unavailable}

if #available(iOS 9, OSX 10.10, *) {    // Use iOS 9 APIs on iOS, and use OS X v10.10 APIs on OS X} else {    // Fall back to earlier iOS and OS X APIs}

详细原文请查看

https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/ControlFlow.html#//apple_ref/doc/uid/TP40014097-CH9-ID120