Osheep

时光不回头,当下最重要。

Swift - 基本语法(三)

一.Swift函数的基本写法

func sayHello(name:String) -> String {
    let result = "Hello," + name + "!"
    return result
}

sayHello(name: "Sunshine") // 函数返回的结果是:Hello,Sunshine!

// 函数名:sayHello
// 参数列表:name - 参数名 String - 参数类型
// 返回值:String - 返回值的参数类型

因为 name有可能为nil,所以函数的name应该是可选类型:

func sayHello(name:String?) -> String {
    let result = "Hello," + (name ?? "Guest") + "!"
    return result
}

var nickname:String?
nickname = "Sunshine"
print(sayHello(name: nickname))

二.使用元组返回多个值

// 返回值不一定要给返回的名字的 但是还是建议加上 增强代码的可读性
var userScores:[Int] = [12,999,666,7687,9999,1024,2567]
func maxmainScores(scores:[Int]) -> (maxScores:Int, mainScores:Int)? {
    // 在实际项目中 读取到的数组userScores可能为nil 所以函数返回的元组也是一个可选类型 如果数组为nil,就return nil
    if scores.isEmpty {
        return nil
    }
    var maxScore = scores[0], minScore = scores[0]
    for score in scores {
        maxScore = max(maxScore, score)
        minScore = min(minScore, score)
    }
   return(maxScore,minScore)
}
print("测试 - \(maxmainScores(scores: userScores))") // 打印的结果:测试 - (maxScores: 9999, mainScores: 12)

Q:在实际开发中可能会遇到userScores没有数据就返回nil的情况,该如何改进程序?

var userScores:[Int]? = [12,999,666,7687,9999,1024,2567]
userScores = userScores ?? []
func maxmainScores(scores:[Int]) -> (maxScores:Int, mainScores:Int)? {
    if scores.isEmpty {
        return nil
    }
    var maxScore = scores[0], minScore = scores[0]
    for score in scores {
        maxScore = max(maxScore, score)
        minScore = min(minScore, score)
    }
    return(maxScore,minScore)
}
print("测试 - \(maxmainScores(scores: userScores!))") // 打印的结果:测试 - (maxScores: 9999, mainScores: 12)

三. 参数的默认值

// 在参数类型后面加上: ‘ ="Hello"’表示greeting这个参数默认值为Hello 调用的时候去掉greeting参数即可。
func sayHello(name:String,greeting:String = "Hello",others:String) -> String {
    let result = greeting + "," + name + others + "!"
    return result
}
print("测试 - \( sayHello(name: "Sunshine", others: " And Candy"))")

四.可变参数

// Others:Int...:表示可以传任意多个参数 一个函数只能有一个可变参数
func add(a:Int, b:Int, Others:Int...) -> Int {
    var result = a + b
    for number in Others {
        result += number
    }
    return result
}

var result0 = add(a: 1, b: 2, Others: 3,4,5)
var result1 = add(a: 1, b: 2)
print("测试 - \(result1)")

五.常量参数、变量参数和inout参数

Q:如何把十进制的数据转化成二进制的数据,并且以字符串的形式打印出来?

func toBinary(num:Int) -> String {
    var num = num
    var result:String = ""
    while num != 0 {
        result = String(num%2) + result
        num = num/2
    }
    return result
}

let result = toBinary(num: 6)
print("测试 - \(result)") // 打印结果是:110

Q:如何交换两个变量?

func swapTwoInts( a:inout Int, b:inout Int) {
    var c = a
    a = b
    b = c
}

var x = 10, y = 8
swapTwoInts(a: &x, b: &y)
print("测试 - \(x,y)") // 最后的打印结果:测试 - (8, 10)
// inout:告诉系统我传入的参数不是要存入副本的 而是实实在在改变它的值的 相当于C语言里面的址传递

等价于:

var x = 10, y = 8
swap(&x, &y)
print("测试 - \(x,y)") // 最后的打印结果:测试 - (8, 10)

六.函数类型

func add(a:Int, b:Int) -> Int {
    return a + b
}
let anotherAdd:(Int,Int) -> Int = add // 让一个常量为函数类型
print("测试 - \(anotherAdd(Int(4.0), 6))")

func sayHello(nickName:String){
    print("Hello," + nickName)
}
let anotherSayHello:(String)->() = sayHello
anotherSayHello("Sunshine")

func sayHi(){
    print("Sunshine")
}
let anotherSayHi:()->() = sayHi
anotherSayHi()

Q: 如何定义函数的类型?

//  有参数值 有函数有返回值
let anotherAdd:(Int,Int) -> Int = add 
// 有参数值 没有函数返回值 ->()不能省略
let anotherSayHello:(String)->() = sayHello 
//没有参数值 没有函数返回值
let anotherSayHi:()->() = sayHi 
//没有参数值 没有函数返回值
let anotherSayHi:()->Void = sayHi 

栗子:

func changeScores(op:(Int) -> Int,scores:inout [Int]) {
    for i in 0..<scores.count {
        scores[i] = op(scores[i])
    }
}
func op1(x:Int)->Int {
    return Int(sqrt(Double(x))*10)
}
func op2(x:Int)->Int {
    return Int(Double(x)/150.0 * 100.0)
}
func op3(x:Int)->Int {
    return x + 3
}

var scores1 = [36,61,78,89,99]
changeScores(op: op1, scores: &scores1)
print("测试 - \(scores1)") //  测试 - [60, 78, 88, 94, 99]

var scores2 = [88,99,108,128,150]
changeScores(op: op2, scores: &scores2)
print("测试 - \(scores2)") //  测试 - [58, 66, 72, 85, 100]

var scores3 = [59,60,77,87,95]
changeScores(op: op3, scores: &scores3)
print("测试 - \(scores3)") // 测试 - [62, 63, 80, 90, 98]

七.闭包的基本语法

var arr = [1,3,5,7,9,8,10,0]
arr.sort() // 无返回值 此时的arr已经按照从小到大的顺序排列
arr.sorted() // 有返回值 返回的结果即是从小到大的顺序排列之后的数组

// 闭包的写法
{(a:Int,b:Int) -> Bool in
    // 具体要执行的代码 Bool表示返回值
}

栗子:

var strArr = ["d","cd","bcd","abcd","ab","a"]
strArr.sort { (str1, str2) -> Bool in
    if(str1.characters.count != str2.characters.count) {
        return  str1.characters.count < str2.characters.count
    }
    return str1 < str2
}
print("测试 - \(strArr)") //  打印结果:测试 - ["a", "d", "ab", "cd", "bcd", "abcd"]

八.使用闭包简化语法

var arr = [1,3,5,7,9,8,10,0]
func compareTwoInts(a:Int,b:Int) -> Bool {
    return a > b
}
//arr.sort { (a, b) -> Bool in return a > b}
//print("测试 - \(arr)")
// 简化写法1:(闭包里面的逻辑只有一句话的时候才可以这么省略)
arr.sort { a, b in return a > b}
print("测试 - \(arr)")

// 简化写法2:
arr.sort { a, b in a > b}
print("测试 - \(arr)")

九.值类型和引用类型

func tryToChangeValue( x :Int) {
    var x = x
    x += 1
}
var num = 6
tryToChangeValue(x: num) //  x = 6 没发生变化 说明是值类型

引用类型:function(函数)/closure(闭包)

func calcTotalMiles(todayMiles:Int) -> () -> Int {
    var totalMiles = 0
    return {
        totalMiles += todayMiles
        return totalMiles
    }
}

栗子:

var dailyTwoMiles = calcTotalMiles(todayMiles: 10)
dailyTwoMiles() // 10
let result = dailyTwoMiles() // 20
print("测试 - \(result)") // 20

var myplan = dailyTwoMiles
let myresult1 = myplan()
print("测试 - \(myresult1)")// 30

dailyTwoMiles()
let myresult2 = myplan()
print("测试 - \(myresult2)")// 50 myplan发生了改变 说明是引用类型

十.枚举的基本用法

enum gameEnding {
    case Win
    case Lose
    case Draw
}
var yourScore = 100
var enemyScore = 100
var theGameEnding:gameEnding
if yourScore > enemyScore {
    theGameEnding = gameEnding.Win
}else if yourScore == enemyScore {
    theGameEnding = .Draw
}else {
    theGameEnding = .Lose
}

switch theGameEnding {
case .Win:
    print("测试 - Win")
case .Lose:
    print("测试 - Lose")
case .Draw:
    print("测试 - Draw")
}

十一.枚举类型关联默认值

enum Months:Int {
    case Jan = 1,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec
}
let curMonth:Months = .Nov
let rawValue = curMonth.rawValue
print("测试 - \(rawValue)") // 11

let nextMonth:Months? = Months.init(rawValue: 12)
print("测试 - \(nextMonth!.rawValue)") // 12

十二.更加灵活的枚举使用方式:枚举里面可以存储不同类型的值

enum barCode {
    case UPCA(Int,Int,Int,Int)
    case QRCode(String)
}
let proCodeA = barCode.UPCA(4, 102, 345, 6)
let proCodeB:barCode = .QRCode("This is a informaton")

switch proCodeA {
case .UPCA(let number1, let number2, let number3, let number4):
    print("测试 - \(number1)\(number2)\(number3)\(number4)")
default:
    print("测试 - This is an information")
}
点赞