for in

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

let base = 3
let power = 10
var answer = 1
for _ in 1...power {
    answer *= base
}

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

While 循环

//while 循环通过判断单一的条件开始。如果条件为 true ，语句的合集就会重复执行直到条件变为 false 。
while condition {
     statements
}

repeat-while 循环(do while)

repeat {
    statements
} while condition

repeat {
    // move up or down for a snake or ladder
    square += board[square]
    // roll the dice
    diceRoll += 1
    if diceRoll == 7 { diceRoll = 1 }
    // move by the rolled amount
    square += diceRoll
} while square < finalSquare
print("Game over!")

Switch(相比 C 和 Objective-C 里的 switch 语句来说，Swift 里的 switch 语句不会默认从每个情况的末尾贯穿到下一个情况里。相反，整个 switch 语句会在匹配到第一个 switch 情况执行完毕之后退出，不再需要显式的 break 语句。这使得 switch 语句比 C 的更安全和易用，并且避免了意外地执行多个 switch 情况。)

let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a", "A":
    print("The letter A")
default:
    print("Not the letter A")
}
// Prints "The letter A"

let approximateCount = 62
let countedThings = "moons orbiting Saturn"
var naturalCount: String
switch approximateCount {
case 0:
    naturalCount = "no"
case 1..<5:
    naturalCount = "a few"
case 5..<12:
    naturalCount = "several"
case 12..<100:
    naturalCount = "dozens of"
case 100..<1000:
    naturalCount = "hundreds of"
default:
    naturalCount = "many"
}
print("There are \(naturalCount) \(countedThings).")
// prints "There are dozens of moons orbiting Saturn."

元组 (元组竟然是控制流～～)

//你可以使用元组来在一个 switch 语句中测试多个值。每个元组中的元素都可以与不同的值或者区间进行匹配。另外，使用下划线（ _）来表明匹配所有可能的值。
//下边的例子接收一个 （x,y） 点坐标，用一个简单的元组类型 (Int,Int) ，并且在后边显示在图片中：
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")
}
//元组 值绑定:switch 情况可以将匹配到的值临时绑定为一个常量或者变量，来给情况的函数体使用。这就是所谓的值绑定，因为值是在情况的函数体里“绑定”到临时的常量或者变量的。
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))")
}

// switch 情况可以使用 where 分句来检查额外的情况。
下边的栗子划分 (x,y) 坐标到下边的图例中：
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")
}
//复合情况：多个 switch 共享同一个函数体的多个情况可以在 case 后写多个模式来复合，在每个模式之间用逗号分隔。如果任何一个模式匹配了，那么这个情况都会被认为是匹配的。如果模式太长，可以把它们写成多行，比如说：
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"

let stillAnotherPoint = (9, 0)
switch stillAnotherPoint {
case (let distance, 0), (0, let distance):
    print("On an axis, \(distance) from the origin")
default:
    print("Not on an axis")
}
// Prints "On an axis, 9 from the origin"

//控制转移语句
//continue: 跳过
//break:跳出
//fallthrough：贯穿
//return：结束
//throw：抛出异常