Swift7 - 循环、函数

// for 循环
let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names {
    print("Hello, \(name)!")
}

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

let base = 3
let power = 10
var answer = 1
for _ in 1...power {
    answer *= base
}
print("\(base) to the power of \(power) is \(answer)")

// 半开区间运算符 ..<
let minutes = 60
for tickMark in 0..<minutes {
    //不包括60
}

let minuteInteval = 5
for tickMark in stride(from: 0, to: minutes, by: minuteInteval) {
    // （0, 5, 10, 15 ... 45, 50, 55）
}

let hours = 12
let hourInterval = 3
for tickMark in stride(from: 3, through: hours, by: hourInterval) {
    // 3, 6, 9, 12
}

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

let anotherPoint = (2, 0)
switch anotherPoint {
    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 a y value of \(y)")
    case (let x, let y):
        print("somewhere else at (\(x), \(y))")
}

let 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")
}

//返回值是元组
func minMax(array: [Int]) -> (min: Int, max: Int)? {
    if array.isEmpty { return nil }
    var currentMin = array[0]
    var currentMax = array[0]
    
    for value in array[1..<array.count] {
        if value < currentMin {
            currentMin = value
        } else if value > currentMax {
            currentMax = value
        }
    }
    return (currentMin, currentMax)
}

if let bounds = minMax(array: [8, -6, 2, 109, 3, 77]) {
    print("min is \(bounds.min) and max is \(bounds.max)")
}

//可变参数,一个函数最多只能拥有一个可变参数。
func arithmeticMean(_ numbers: Double...) -> Double {
    var total: Double = 0
    for number in numbers {
        total += number
    }
    return total / Double(numbers.count)
}
arithmeticMean(1, 2, 3, 4, 5)

//输入输出参数:函数可以修改参数的值，并且想要在这些修改在函数调用结束后仍然存在
func swaoTwoInts(_ a: inout Int, _ b: inout Int) {
    let temporaryA = a
    a = b
    b = temporaryA
}

var someInt = 3
var anotherInt = 104
swap(&someInt, &anotherInt)
print("someInt is now \(someInt), and anotherInt is now \(anotherInt)")


//使用函数类型
func addTwoInts(_ a: Int, _ b: Int) -> Int {
    return a + b
}
func multiplyTwoInts(_ a: Int, _ b: Int) -> Int {
    return a * b
}
//”定义一个叫做 mathFunction 的变量，类型是‘一个有两个 Int 型的参数并返回一个 Int 型的值的函数’，并让这个新变量指向 addTwoInts 函数”。
var mathFunction: (Int, Int) -> Int = addTwoInts
print("Result: \(mathFunction(2, 3))")
mathFunction = multiplyTwoInts
print("Result: \(mathFunction(2, 3))")

func chooseStepFuntion(backward: Bool) -> (Int) -> Int {
    func stepForward(intput: Int) -> Int {
        return intput + 1
    }
    func stepBackward(input: Int) -> Int {
        return input - 1
    }
    return backward ? stepBackward : stepForward
}
var currentValue = -4
let moveNearerToZero = chooseStepFuntion(backward: currentValue > 0)
while currentValue != 0 {
    print("\(currentValue)...")
    currentValue = moveNearerToZero(currentValue)
}
print("Zero!")