五、控制流

控制流主要关键字

• while、repeat-while 循环
• if、guard、switch 基于特定的条件执行不同的代码分支
• continue、break 传递执行流到另一个点

循环语句

For-in循环

1. 遍历数组

let nameArr = ["lujianyong","gongxun","huangwei","dundekui","ziqiang"]

for name in nameArr {
    print(name)
}

2. 遍历字典

let numRomanDic = ["1":"one","2":"two","3":"three","4":"four"]
for (key, value) in numRomanDic {
    print("\(key):\(value)")
}

3. 遍历数字区间

for index in 1...20 {
    print(index)
}

//计算base的指数power的结果answer的值
let base = 2
let power = 10
var answer = 1

for index in 1...10 {
    answer *= base
}

print("\(base) to the power of \(power) is \(answer)")

index 在每次遍历循环的时候自动设置，隐式地在循环的生命中声明了， 所以不需要在使用之前声明
如果不需要index，也可以用下划线(_)代替

4. 循环跳过标记

let maxValue = 30
let minuteInterval = 5

//stride(from: , to: , by: ) 跳过标记  开区间
for tickMark in stride(from: 0, to: maxValue, by: minuteInterval) {
    print(tickMark)
}//输出：0\n    5\n   10\n  15\n   20\n  25\n

//stride(from: , through: , by: ) 跳过标记  闭区间
for tickMark in stride(from: 0, through: 30, by: minuteInterval) {
    print(tickMark)
}//输出：0\n    5\n   10\n  15\n   20\n  25\n  30\n

while循环

• 循环执行一个语句直到条件变成false结束（主要用于当循环次数不确定时）：
• while在每次循环开始时计算条件； repeat-while在每次循环结束时计算条件
  爬梯游戏帮助我们更好地理解

//爬梯子游戏
let finalSquare = 30
var board = Array.init(repeating: 0, count: finalSquare+1)

board[03] = +08;board[06] = +11;board[09] = +09;board[10] = +03;board[11] = -10;
board[14] = -10;board[19] = -11;board[22] = -02;board[24] = -08;board[28] = -08;

var square = 0
var dicRoll = 0

while square < finalSquare {
    //roll the dice 掷骰子模拟
    dicRoll += 1
    if dicRoll == 7 {
        dicRoll = 1
    }
    //move by the rolled amout 移动至指定格子
    square += dicRoll
    
    //判断是否超出越界 以及是否有梯子
    if square<board.count {
        square += board[square];
    }
    print(square,dicRoll)
}

print("game over")

repeat{
    //move up or dowm for a snake or ladder 当前格子的移动情况
    square += board[square]
    
    //掷骰子
    dicRoll += 1
    if dicRoll == 7 {
        dicRoll = 1
    }
    square += dicRoll
    
    print(square,dicRoll)
}while square < finalSquare

print("game over")

let arr = [10, -10, 20, -3, 0, 65, 34, -12]

for num in arr where num > 0{
    print(num)//输出：10 20 65 34
}

While循环也可以添加where 过滤作用，不是循环结束的条件

条件语句

1. if 和OC一样
2. Switch..case..default

//常规匹配
let char :Character = "a"

switch char {
case "a","A":
    print("The letter A")
case "b","B",
     "c","C":
    print("The letter B/C")
default:
    print("The Another letter")
}

//不包含default 但是包含所有情况
enum Answer {
    case right
    case wrong
}
let answer = Answer.wrong
switch answer {
    case Answer.right:
        print("Answer.right")
    case .wrong://由于已确定answer类型，可以省略Answer
        print("Answer.wrong")
}

//区间匹配
let approximateCount = 151
let countedThings = "heros"
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)")//There are hundreds of heros

//元组匹配
//每个元组中的元素都可以与不同的值或者区间进行匹配
//使用下划线（_）来表明匹配所有可能的值

//决定坐标是否在原点（0,0）;在X轴；在Y轴；在4*4并以原点为中心的方格中；或者在方格外面

let somePoint = (-3,2)

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 on the box")
    default:
        print("(\(somePoint.0),\(somePoint.1)) is outside of the box")
}

//在case的情况的函数体里“绑定”到临时的常量或者变量

//决定坐标是否在X轴；在Y轴；或者在其他地方

let somePoint = (-3,2)

switch somePoint {
    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,y):
        print("somewhere else at (\(x),\(y))")
}

//决定坐标是否在x == y；还是在x== -y；或者在其他地方

let somePoint = (-1,9)
//Switch 情况可以使用 where 分句来检查额外的情况
switch somePoint {
    case let (x,y) where x == y:
        print("(\(x),\(y)) is one the line x == y")
    case let (x,y) where x == -y:
        print("(\(x),\(y)) is one the line x == -y")
    case let (x,y):
        print("(\(x),\(y)) is just some arbitrary point")
}

【注意】与OC不同的点:
if后面的条件省略小括号，大括号不可省略 if 后只能是bool类型
没有隐式贯穿 不再需要显式的break语句 case后不能写大括号({})! 如果需要贯穿 需要使用fallthrough关键字
Switch需要保证能处理所有情况，且每个情况都必须包含可执行语句 不能同时匹配多个分支 （但可以将多个情况的写在一个case中）
Switch也支持Character，String，区间，元组匹配
Switch 情况可以使用 where 分句来检查额外的情况

控制转移语句

• continue break fallthrough（循环控制）
• return（函数）
• throw（抛出函数传递错误）
• fallthrough （贯穿case）
• guard (提前退出)

//给循环语句打标签

let finalSquare = 30
var board = Array.init(repeating: 0, count: finalSquare+1)

board[03] = +08;board[06] = +11;board[09] = +09;board[10] = +03;board[11] = -10;
board[14] = -10;board[19] = -11;board[22] = -02;board[24] = -08;board[28] = -08;

var square = 0
var dicRoll = 0

gameLoop: while square < finalSquare {
    //roll the dice 掷骰子模拟
    dicRoll += 1
    if dicRoll == 7 {
        dicRoll = 1
    }
    
    //move by the rolled amout 移动至指定格子
    switch square + dicRoll {
    case finalSquare:
        break gameLoop
    case let newSquare where newSquare > finalSquare:
        square += 1//防止死循环 只要骰子超出则只跳一格
        continue gameLoop
    default:
        square += dicRoll
        square += board[square]
    }

    print(square,dicRoll)
}

print("game over")

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 id nice near you")
        return
    }
    
    print("I hope the weather id nice in \(location)")
}

greet(person: [:])
greet(person: ["name":"john"])
greet(person: ["name":"mike","location":"Beijing"])
/*
Who are you?
hello john
I hope the weather id nice near you
hello mike
I hope the weather id nice in Beijing
*/

【注意】Swift去除了 ++、-- 运算符

Swift学习日记5.0