<<Swift巩固笔记>> 第5篇 控制流

循环语句

for…in 循环

// 遍历数组 (Array)
let names = ["zero", "hour", "ray", "lee"]
for name in names {
    print("Hello, \(name)!")
}

// 遍历字典 (Dictionary)
let animalLegs = ["spider":8, "ant":6, "cat":4]
for (name, legCount) in animalLegs {
    print("\(name) has \(legCount) legs")
}

// 遍历区间 (Range)
let range = 1...5
for i in range {
    print("\(i) times 5 is \(i * 5)")
}// 忽略区间内每一项的值 _
var answer = 1
for _ in range {
    answer *= 3
}
print("3 to the power of 5 is \(answer)")

while循环

while currentWrongCount < 5 {
    print("请输入密码")
    let input = readLine()
    if input == "123456" {
        print("密码正确")
        currentWrongCount = 5
    } else {
        print("密码错误")
        currentWrongCount += 1
    }
}

repeat…while 循环

repeat {
    print("请输入密码")
    let input = readLine()
    if input == "123456" {
        print("密码正确")
        currentWrongCount = 5
    } else {
        print("密码错误")
        currentWrongCount += 1
    }
} while currentWrongCount < 5

条件语句

if 语句

// if 语句
let isGirl = true
if isGirl {
    print("我们出去玩会吧!")
}

// if...else
if isGirl {
    print("我们去电影院看电影啊!")
} else {
    print("我们用电脑看电影吧!")
}

// if...else if...else 最后一个else可以省略
let score = 40
if score >= 90 {
    print("你成绩好好哟!")
} else if score >= 80 {
    print("成绩不错呀, 咋学的?")
} else if score >= 70 {
    print("可以啊兄弟, 加把劲儿!")
} else {
    print("猪!")
}

switch…case语句

let someChar: Character = "b"
switch someChar {
case "a":
        print("first character")
case "z":
        print("last character")
default:
        print("other character")
}

同时匹配多个值

switch someChar {
case "a", "A":
    print("letter a or A")
default:
    print("not the letter a or A")
}

区间匹配

let count = 62
let naturalCount: String
switch count {
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(naturalCount)

元组的匹配

let point = (1, 1)
switch point {
case (0, 0):
    print("\(point) is at the origin")
case (_, 0):
    print("\(point) is at the x-axis")
case (0, _):
    print("\(point) is at the y-axis")
case (-2...2, -2...2):
    print("\(point) is inside the box")
default:
    print("\(point) is outside the box")
}

值绑定 Value Bindings

// case分支允许将匹配的值声明为常量或变量, 并且在分支体内使用 - 这种行为称为值绑定
let anotherPoint = (2, 0)
switch anotherPoint {
case (let x, 0):
    print("在x轴上\(x)处")
case (0, let y):
    print("在y轴上\(y)处")
case let (x, y):
    print("在(\(x), \(y))处")
}

where的使用

let anyPoint = (1, -1)
switch anyPoint {
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 a common point)")
}

复合型cases

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 consonant")
}

复合 + 值绑定

let stillPoint = (3, 0)
switch stillPoint {
case (let distance, 0), (0, let distance):
    print("在坐标轴上, 距离原点\(distance)")
default:
    print("不在坐标轴上")
}

控制转移语句

continue语句

// 停止本次循环, 开始下次循环
let hiStr = "hello, swift"
var output = ""
for character in hiStr {
    switch character {
    case "a", "e", "i", "o", "u":
        continue
    default:
        output.append(character)
    }
}
print(output)

break 语句

// 立即结束整个循环
for index in 1...5 {
    if index == 3 {
        break
    } else {
        print(index)
    }
}

fallthrough 语句

// 从上一个case分支中跳转到下一个case分支中
let integerValue = 5
var desc = "The number \(integerValue) is"
switch integerValue {
case 2, 3, 5, 7, 11, 13, 17, 19:
    desc += " a prime number, and also"
    fallthrough
default:
    desc += " an integer."
}
print(desc)

带标签的语句 statement label

loop: for i in 1...3 {
    print("第\(i)次循环")
    switch i {
    case 1:
        continue
    case 2:
        break loop // 在这里如果想要跳出for循环, 就要用到带标签的循环语句
    default:
        print("default")
    }
}

guard语句

// 条件为真时, 执行guard语句后的代码, 否则执行else语句
func greet(person: [String: String]) {
    guard let name = person["name"] else {
        return
    }
    print("Hello, \(name)!")
    
    guard let location = person["location"] else {
        print("I hope the weather is nice near you")
        return
    }
    print("I hope the weather is nice in \(location)")
}
greet(person: ["name":"Ray", "location":"BJ"])