一、函数的基本使用

//1、无参无返回值的函数
func about(){
    print("iphone7")
}
about()

func about1() -> Void  {
  print("iphone7")
}
about1()

//2、无参有返回值的函数
func readMessage() -> String{
    return "吃饭了吗"
}
print(readMessage())


//3、有参无返回值的函数
func callPhone(phoneNum: String){
     print("打电话\(phoneNum)")
}
callPhone(phoneNum: "15669993907")


//4、有参数有返回值的函数
func sum(num1: Int, num2: Int) -> Int{
    return num1 + num2
}
print(sum(num1: 3, num2: 2))


//5、多参数多返回值的函数
func minMax(num1: Int, num2: Int, num3: Int) -> (min: Int, max: Int) {
    var max: Int
    var min: Int
    
    max = ( (num1 > num2 ? num1 : num2) > num3) ? (num1 > num2 ? num1 : num2) : num3;
    min = ( (num1 > num2 ? num2 : num1) > num3) ? num3 : (num1 > num2 ? num2 : num1);
    
    return (min, max)
    
}
print(minMax(num1: 10, num2: 8, num3: 16))

二、函数的使用注意 --- 参数名

//省略参数标签
func buySomeThing(_ vegetables: String, money: Int) -> String {
   return "我买了\(vegetables),花了\(money)元"
}
print(buySomeThing("苹果", money: 120))


//默认形式参数值
func buy(parameter: Int = 12) {
    print("花了\(parameter)")
}
buy(parameter: 6)
buy()

//可变形式参数
func sumNumber(_ numbers: Double...) -> Double {
    var total: Double = 0
    for number in numbers {
        total += number
    }
    return total / Double(numbers.count)
}
print(sumNumber(1, 2, 3, 4, 5))

//输入输出形式参数  值传递转换为指针传递
func swapTwoInts(_ a: inout Int, _ b: inout Int) {
    let temporaryA = a
    a = b
    b = temporaryA
}
var someInt = 3
var anotherInt = 107
swapTwoInts(&someInt, &anotherInt)
print("someInt is now \(someInt), and anotherInt is now \(anotherInt)")

三、函数的使用注意 --- 函数类型

//这个函数的类型都是 (Int, Int) -> Int
func addTwoInts(_ a: Int, _ b: Int) -> Int {
    return a + b
}

//使用函数类型 --- 它的类型是‘一个能接受两个 Int值的函数，并返回一个 Int值
var mathFunction: (Int, Int) -> Int = addTwoInts
print("Result: \(mathFunction(2, 3))")


//函数类型作为形式参数
func printMathResult(_ mathFunction: (Int, Int) -> Int, _ a: Int, _ b: Int) {
    print("Result: \(mathFunction(a, b))")
}

printMathResult(addTwoInts, 3, 5)


//函数类型作为返回类型  --- 写法是在函数的返回箭头（ ->）后立即写一个完整的函数类型。

//这两个函数的类型都是 (Int) -> Int
func stepForward(_ input: Int) -> Int {
    return input + 1
}

func stepBackward(_ input: Int) -> Int {
    return input - 1
}


func chooseStepFunction(backwards: Bool) -> (Int) -> Int {
    return backwards ? stepBackward : stepForward
}

var currentValue = 3
let moveNearerToZero = chooseStepFunction(backwards: currentValue > 0)

print(moveNearerToZero)

while currentValue != 0 {
    print("\(currentValue)... ")
    currentValue = moveNearerToZero(currentValue)
}

四、函数嵌套

func chooseFunction(backwards: Bool) -> (Int) -> Int {
    func forward(input: Int) -> Int { return input + 1 }
    func backward(input: Int) -> Int { return input - 1 }
    return backwards ? backward : forward
}


var currenValue = -4
let nearerToZero = chooseStepFunction(backwards: currentValue > 0)

while currenValue != 0 {
    print("\(currentValue)... ")
    currentValue = nearerToZero(currentValue)
}