Swift 控制流

For - in 循环

import UIKit

// For - in 循环
// 闭区间
for index in 1...5 {
    print("\(index) times 5 is \(index * 5)")
}

// 数组
var namesArray = ["Jordan", "Kobe", "Wade"]
for name in namesArray {
    print("Hello, \(name)!")
}

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

console log 如下

For-in循环.png

while 循环

// while 循环 (先判断条件，在执行语句)
var i = 0
while i < 10 {
    i += 1
    print("While 第\(i)次循环")
}

console log 如下

while循环.png

repeat - while 循环

// repeat - while 循环 (先执行语句，在判断条件)
var j = 11
repeat {
    j += 1
    print("repeat While 第\(j)次循环")
} while j < 10

console log 如下

repeat-while循环.png

if 条件语句
// if 条件语句
var temperaturInFahrenheit = 40
if temperaturInFahrenheit < 32 {
    print("It's very cold. Consider wearing a scarf.")
} else {
    print("It's not that cold. Wear a t-shirt")
}

console log 如下

if条件语句.png

switch 常规用法(case 分支里面必须有语句，默认只执行一个分支，不用写break)

// switch 常规用法
var someCharacter : Character = "a"
switch someCharacter {
case "a", "A" :
    print("The letter a")
case "b" :
    print("The letter b")
default :
    print("The other letter")
}

console log 如下

switch常规用法.png

switch 区间匹配

// switch 区间匹配
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)")

console log 如下

switch区间匹配.png

switch 元组匹配

// switch 元组匹配
var somePoint = (1, 1)

switch somePoint {
case (0, 0):
    print("(0, 0) is at the origin")
case (_, 0):
    print("(\(somePoint.0), 0) is at the x-axis")
case (0, _):
    print("(0, \(somePoint.1)) is at 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 the box")
}

console log 如下

switch 元组匹配.png

switch 元组值绑定

// switch 元组值绑定
var otherPoint = (1, 5)
switch otherPoint {
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 an y value of \(y)")
case (let x, let y):
    print("somewhere else at (\(x), \(y))")
}

console log 如下

switch 元组值绑定.png

switch 元组值绑定where 筛选

// switch 元组值绑定where 筛选
var 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")
}

console log 如下

switch 元组值绑定where 筛选.png

continue 关键字

// continue 关键字
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)

console log 如下

continue 关键字.png

fallthrough 关键字

// fallthrough 关键字
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
default:
    description += " an integer."
}
print(description)

console log 如下

fallthrough 关键字.png