func greet(person: String) -> String {
    let greeting = "Hello, " + person + "!"
    return greeting
}

func greetAgain(person: String) -> String {
    return "Hello again, " + person + "!"
}

print(greet(person: "Anna"))
// Prints "Hello, Anna!"
print(greet(person: "Brian"))
// Prints "Hello, Brian!"

print(greetAgain(person: "Anna"))
// Prints "Hello again, Anna!"

func sayHelloWorld() -> String {
    return "hello, world"
}

print(sayHelloWorld())
// Prints "hello, world"

func greet(person: String, alreadyGreeted: Bool) -> String {
    if alreadyGreeted {
        return greetAgain(person: person)
    } else {
        return greet(person: person)
    }
}

print(greet(person: "Tim", alreadyGreeted: true))
// Prints "Hello again, Tim!"

func greet(person: String) {
    print("Hello, \(person)!")
}

greet(person: "Dave")
// Prints "Hello, Dave!"
// 반환 값이 필요 없기 때문에, 함수의 정의는 반환 화살표(->)나 반환 타입을 포함하지 않는다.

func printAndCount(string: String) -> Int {
    print(string)
    return string.count
}
func printWithoutCounting(string: String) {
    let _ = printAndCount(string: string)
}

printAndCount(string: "hello, world")
// prints "hello, world" and returns a value of 12
printWithoutCounting(string: "hello, world")
// prints "hello, world" but does not return a value

func minMax(array: [Int]) -> (min: Int, max: Int) {
    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)
}

let bounds = minMax(array: [8, -6, 2, 109, 3, 71])
print("min is \(bounds.min) and max is \(bounds.max)")
// Prints "min is -6 and max is 109"

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, 71]) {
    print("min is \(bounds.min) and max is \(bounds.max)")
}
// Prints "min is -6 and max is 109"
// 옵셔널 바인딩을 통해 nil이 반환될 경우에 대처 가능

struct CompactRect {
    var origin = Point()
    var size = Size()
    var center: Point {
        get {
            Point(x: origin.x + (size.width / 2),
                  y: origin.y + (size.height / 2))
        }
        set {
            origin.x = newValue.x - (size.width / 2)
            origin.y = newValue.y - (size.height / 2)
        }
    }

func greeting(for person: String) -> String {
    "Hello, " + person + "!"
}

print(greeting(for: "Dave"))
// Prints "Hello, Dave!"

func anotherGreeting(for person: String) -> String {
    return "Hello, " + person + "!"
}

print(anotherGreeting(for: "Dave"))
// Prints "Hello, Dave!"

func someFunction(firstParameterName: Int, secondParameterName: Int) {
    // In the function body, firstParameterName and secondParameterName
    // refer to the argument values for the first and second parameters.
}

someFunction(firstParameterName: 1, secondParameterName: 2)

func someFunction(argumentLabel parameterName: Int) {
    // In the function body, parameterName refers to the argument value
    // for that parameter.
}

func someFunction(_ firstParameterName: Int, secondParameterName: Int) {
    // In the function body, firstParameterName and secondParameterName
    // refer to the argument values for the first and second parameters.
}

someFunction(1, secondParameterName: 2)

func someFunction(parameterWithoutDefault: Int, parameterWithDefault: Int = 12) {
    // If you omit the second argument when calling this function, then
    // the value of parameterWithDefault is 12 inside the function body.
}

someFunction(parameterWithoutDefault: 3, parameterWithDefault: 6) // parameterWithDefault is 6
someFunction(parameterWithoutDefault: 4) // parameterWithDefault is 12

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)
// returns 3.0, which is the arithmetic mean of these five numbers
arithmeticMean(3, 8.25, 18.75)
// returns 10.0, which is the arithmetic mean of these three numbers

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)")
// Prints "someInt is now 107, and anotherInt is now 3"

func addTwoInts(_ a: Int, _ b: Int) -> Int {
    return a + b
}

func multiplyTwoInts(_ a: Int, _ b: Int) -> Int {
    return a * b
}
// 위 두 함수는 모두 두 개의 Int 타입 매개변수를 인자로 받아 Int 값을 반환한다.
// 함수들의 타입은 (Int, Int) -> Int가 된다.

func printHelloWorld() {
    print("hello, world")
}
// 이 함수의 타입은 () -> Void이다.

func addTwoInts(_ a: Int, _ b: Int) -> Int {
    return a + b
}

func multiplyTwoInts(_ a: Int, _ b: Int) -> Int {
    return a * b
}

var mathFunction: (Int, Int) -> Int = addTwoInts
// addTwoInts(_:_:) 함수는 mathFunction과 같은 타입이기 때문에 Swift의 타입 체커에 의해 할당이 허용

print("Result: \(mathFunction(2, 3))")
// Prints "Result: 5"
// mathFunction으로 할당된 addTwoInts 함수를 다음과 같이 사용

mathFunction = multiplyTwoInts
print("Result: \(mathFunction(2, 3))")
// Prints "Result: 6"
// mathFunction으로 다시 할당된 multiplyTwoInts 함수를 다음과 같이 사용
// 같은 타입을 갖는 다른 함수를 비함수 타입과 동일하게 같은 변수에 할당할 수 있다

let anotherMathFunction = addTwoInts
// anotherMathFunction is inferred to be of type (Int, Int) -> Int
// Swift의 다른 타입처럼, 함수를 상수/변수에 할당할 때 타입 추론을 적용

func printMathResult(_ mathFunction: (Int, Int) -> Int, _ a: Int, _ b: Int) {
    print("Result: \(mathFunction(a, b))")
}
printMathResult(addTwoInts, 3, 5)
// Prints "Result: 8"

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

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

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

var currentValue = 3
let moveNearerToZero = chooseStepFunction(backward: currentValue > 0)
// moveNearerToZero now refers to the stepBackward() function

print("Counting to zero:")
// Counting to zero:

while currentValue != 0 {
    print("\(currentValue)... ")
    currentValue = moveNearerToZero(currentValue)
   // 반환 값으로 moveNearerToZero에 stepBackward가 전달되면서 인수를 전달할 수 있음에 주의
}

print("zero!")
// 3...
// 2...
// 1...
// zero!

func chooseStepFunction(backward: Bool) -> (Int) -> Int {
    func stepForward(input: Int) -> Int { return input + 1 }
    func stepBackward(input: Int) -> Int { return input - 1 }
    return backward ? stepBackward : stepForward
}

var currentValue = -4
let moveNearerToZero = chooseStepFunction(backward: currentValue > 0)
// moveNearerToZero now refers to the nested stepForward() function

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

print("zero!")
// -4...
// -3...
// -2...
// -1...
// zero!