Swift 流程控制

一.for循环

for－in

实例1：

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

1times 5 is 5
2times 5 is 10
3times 5 is 15
4times 5 is 20
5times 5 is 25

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)")

10

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

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)!")
        }

Marry is 10!
Lili is 9!
xiaoming is 12!

二。while循环

语法：

    while condition {

        statements

    }

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

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")
        }

The first letter of the alphabet

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).")
        }

  let numberSymbol: Character = "三"  // Chinese symbol for the number 3
        var possibleIntegerValue: Int?
        switch numberSymbol {
        case "1","?","一","?":
            possibleIntegerValue = 1
        case "2","?","二","?":
            possibleIntegerValue = 2
        case "3","?","三","?":
            possibleIntegerValue = 3
        case "4","?","四","?":
            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."

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

    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"

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"

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"

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"

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."

（编辑：李大同）

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