swift 运算符和控制流程

闭区间运算符

闭区间运算符（a...b）定义一个包含从a到b(包括a和b)的所有值的区间,只能是数字

for index in 1...5 {
    println("\(index) * 5 = \(index * 5)")
}

var names = ["Anna", "Alex", "Brian", "Jack"]
names[2...3] = ["a","b"] //不能添加

半闭区间

半闭区间（a..b）定义一个从a到b但不包括b的区间。方便取数组下标

let names = ["Anna", "Alex", "Brian", "Jack"]
let count = names.count
for i in 0..count {
    println("第 \(i + 1) 个人叫 \(names[i])")
}

for i in 0...count-1{
    println("第 \(i + 1) 个人叫 \(names[i])")
}

闭区间和半闭区间代替了传统的.for循环.使用i++的形式,还可以用于再数组上

fon-in

for-in用来遍历一个区间（range），序列（sequence），集合（collection），系列（progression）里面所有的元素执行一系列语句。

//区间
for index in 1...5 {
    println("\(index) times 5 is \(index * 5)")
}
//数组
let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names {
    println("Hello, \(name)!")
}
//字典
let numberOfLegs = ["spider": 8, "ant": 6, "cat": 4]
for (animalName, legCount) in numberOfLegs {
    println("\(animalName)s have \(legCount) legs")
}
//字符
for character in "Hello" {
    println(character)
}

for-in中index是一个每次循环遍历开始时被自动赋值的常量。这种情况下，index在使用前不需要声明，只需要将它包含在循环的声明中 ，就可以对其进行隐式声明，而无需使用let关键字声明。
index常量只存在于循环的生命周期里。如果你想在循环完成后访问index的值，又或者想让index成为一个变量而不是常量，
你必须在循环之前自己进行声明。

for循环

在初始化表达式中声明的常量和变量（比如var index = 0）只在for循环的生命周期里有效。如果想在循环结束后访问index的值，你必须要在循环生命周期开始前声明index。

for initialization; condition; increment {
statements
}

等同于

  initialization
while condition {
statements
increment
}

switch

switch当匹配后,不会继续执行下一个case,会终止switch语句,所以不需要break语句.如果想要贯穿至特定的 case 分支中，请使用fallthrough贯穿语句
每一个 case 分支都必须包含至少一条语句。代替可以使用","匹配多个case,为同一个值

let someCharacter: Character = "e"
switch someCharacter {
case "a", "e", "i", "o", "u":
    println("\(someCharacter) is a vowel")
case "b", "c", "d",:
    println("\(someCharacter) is a consonant")
default:
    println("\(someCharacter) is not a vowel or a consonant")
}

//case 条件可以是区间,查找一个数字是否在一个区间
switch count {
case 0:
    naturalCount = "no"
case 1...3:
    naturalCount = "a few"
case 4...9:
    naturalCount = "several"
case 10...99:
    naturalCount = "tens of"
case 100...999:
    naturalCount = "hundreds of"
case 1000...999_999:
    naturalCount = "thousands of"
default:
    naturalCount = "millions and millions of"
}

使用元组在同一个switch语句中测试多个值。元组中的元素可以是值，也可以是区间。另外，使用下划线（_）来匹配所有可能的值。
let somePoint = (1, 1)
switch somePoint {
case (0, 0):
    println("(0, 0) is at the origin")
case (_, 0):
    println("(\(somePoint.0), 0) is on the x-axis")
case (0, _):
    println("(0, \(somePoint.1)) is on the y-axis")
case (-2...2, -2...2):
    println("(\(somePoint.0), \(somePoint.1)) is inside the box")
default:
    println("(\(somePoint.0), \(somePoint.1)) is outside of the box")
}

//值绑定
let anotherPoint = (2, 0)
switch anotherPoint {
case (let x, 0):
    println("on the x-axis with an x value of \(x)")
case (0, let y):
    println("on the y-axis with a y value of \(y)")
case let (x, y):
    println("somewhere else at (\(x), \(y))")
}
// 输出 "on the x-axis with an x value of 2"

//使用where
let yetAnotherPoint = (1, -1)
switch yetAnotherPoint {
case let (x, y) where x == y:
    println("(\(x), \(y)) is on the line x == y")
case let (x, y) where x == -y:
    println("(\(x), \(y)) is on the line x == -y")
case let (x, y):
    println("(\(x), \(y)) is just some arbitrary point")
}
// 输出 "(1, -1) is on the line x == -y"

Label

使用break和continue在多重循环或者switch嵌套中跳转

  gameLoop: while square != finalSquare {
    if ++diceRoll == 7 { diceRoll = 1 }
    switch square + diceRoll {
    case finalSquare:
        // 到达最后一个方块，游戏结束
        break gameLoop
    case let newSquare where newSquare > finalSquare:
        // 超出最后一个方块，再掷一次骰子
        continue gameLoop
    default:
        // 本次移动有效
        square += diceRoll
        square += board[square]
    }
}
println("Game over!")