// 遍历区间，返回元素值

for index in ... {

    print("(index) times 5 is (index * 5)")

}

// 循环区间，忽略元素值

for _ in ...power {

    answer *= base

}

// 遍历数组

let names = ["Anna", "Alex", "Brian", "Jack"]

for name in names {

    print("Hello, (name)!")

}

// 遍历字典

let numberOfLegs = ["spider": , "ant": , "cat": ]

for (animalName, legCount) in numberOfLegs {

    print("(animalName)s have (legCount) legs")

}

while square < finalSquare {

    // statements ...

}

// 类似其他语言的do-while语句

repeat {

    // statements ...

} while square < finalSquare

temperatureInFahrenheit =

if temperatureInFahrenheit <=  {

    print("It's very cold. Consider wearing a scarf.")

} else if temperatureInFahrenheit >=  {

    print("It's really warm. Don't forget to wear sunscreen.")

} else {

     print("It's not that cold. Wear a t-shirt.")

}

// person字典中存在key为name的元素时打印name元素值

guard let name = person["name"] else {

    return

}

print("Hello \(name)")

let someCharacter: Character = "z"

switch someCharacter {

case "a":

    print("The first letter of the alphabet")

// case "b": 打开注释后会有编译错误，不存在隐式贯穿

case "c","z":    // 复合匹配

    print("The last letter of the alphabet")

default:

    print("Some other character")

}

// case分支匹配区间

switch approximateCount {

case :

    naturalCount = "no"

case ..<:

    naturalCount = "a few"

default:

    naturalCount = "many"

}

// case分支匹配元组

let somePoint = (, )

switch somePoint {

case (, ):  // 元组元素是值类型

    print("(0, 0) is at the origin")

case (_, ):// 元组元素使用 _ 匹配所有任意值

    print("(\(somePoint.0), 0) is on the x-axis")

case (-..., -...): // 元组元素是区间类型

    print("(\(somePoint.0), \(somePoint.1)) is inside the box")

}

let yetAnotherPoint = (, )

switch yetAnotherPoint {

case (let x, ):

    print("on the x-axis with an x value of \(x)")

case let (x, y) where x == y: // 输出 "(1, -1) is on the line x == y"

    print("(\(x), \(y)) is on the line x == y")

case let (x, y):

    print("(\(x), \(y)) is just some arbitrary point")

}