Swift2.2 學習筆記(十二) ___控制流

For-In

for index in 1...5 {
    //閉區間操作符(...)
    print("\(index) times 5 is \(index * 5)")
    //注意index 常量隻存在于循環的生命周期裡。
}
/*
1 times 5 is 5
2 times 5 is 10
3 times 5 is 15
4 times 5 is 20
5 times 5 is 25
*/           

如果不需要知道範圍内的每一項的值，可以使用下劃線(_)替代變量名來忽略對值的通路

let base = 3
let power = 10
var answer = 1
for _ in 1...power {
    answer *= base  // 3的十次幂
}
print ("\(base) to the power of \(power) is\(answer)")

//3 to the power of 10 is59049           

使用for-in周遊一個數組所有元素

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

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

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

For條件遞增 (for-condition-increment)

for var index = 0; index < 3; ++index {
    print("index is \(index)")
}

var index:Int
for index = 0; index < 3; ++index {
    print("index is \(index)")
}
print("The loop statements were executed \(index) times")           

while 循環

while condition {

statements

}

let finalSqure = 25
var board = [Int](count: finalSqure + 1, repeatedValue: 0)
board[03] = +08; board[06] = +11; board[09] = +09; board[10] = +02
board[14] = -10; board[19] = -11; board[22] = -02; board[24] = -08

var square = 0
var diceRoll = 0
while square < finalSqure {

    if ++diceRoll == 7 { diceRoll = 1 }

    square += diceRoll

    if square < board.count {

        square += board[square]
    }
}
print("GameOver!")
           

Do-While

do {

statements

} while condition

//條件語句
//If
var temperatureInFahrenheit = 30
if temperatureInFahrenheit <= 32 {
    print("it's very cold. Consider wearing a scarf")
}

// Switch
let somCharacter:Character = "e"
switch somCharacter {
    case "a","b":
    print("1")
    case "c","d","e":
    print("2")
    default:
    print("nothing")
}
           

元祖，在同一個switch語句中測試多個值。元組中的元素可以是值，也可以是範圍。使用(_)來比對所有可能的值

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")

    //    (1,1) is inside the box

}           

值綁定

case塊的模式允許将比對的值綁定到一個臨時的常量或者變量，這些常量或變量在該case塊裡就可以被引用了

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("somewhee else at (\(x),\(y))")

    // on the x-axis with an x value of 2
}
           

Where

case塊的模式可以使用where語句來判斷額外的條件

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 linx x == -y)")
case let (x,y):
    print("(\(x),\(y) is just some arbirthary point)")

    //    (1,-1 is on the linx x == -y)


}
           

Swift四種控制轉移語句

-continue

-break

-fallthrough

-return

//continue 語句告訴循環停止正在做的事情并且再次從開始循環的下一次周遊。就是說“我不再繼續目前的循環周遊了”而不是離開整個的循環
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)  //grt mnds thnk lk           

Break 立即結束整個控制流語句。

當在switch語句裡使用時，break 導緻 switch 語句立即結束它的執行，并且轉移控制到 switch 語句結束花括号（ ｝）之後的第一行代碼上

let numberSymbol: Character = "三"
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).")
}
//The integer value of 三 is 3.           

Fallthrough

如果你确實需要 C 風格的貫穿行為，你可以選擇在每個情況末尾使用 fallthrough 關鍵字。

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
//   使用 fallthrough 關鍵字來“貫穿到” default 情況。 default 情況添加額外的文字到描述的末尾，接着 switch 語句結束。
default:
    description += "an integer."
}
print(description)