var gender = ""
gender = "man"
switch gender {
case "man":
  print("man")
  case "female":
  print("female")
default:
  print("other")
}

enum Gender {
  case man
  case female
  case other
}
var gType: Gender = .man
switch gType {
case .man:
  print("男性")
case .female:
  print("女性")
case .other:
  print("其他类型")
default:
  print("我也不知道")
}

var customText: String?
var defaultText = "您好"
var textToUse = ""
if let text = customText {
  textToUse = text
} else {
  textToUse = defaultText
}

var customText: String?
var defaultText = "您好"
var textToUse = ""
var textToUse = customText ?? defaultText

var arr = [Int]()
for i in 1...10 {
  if i % 2 == 1 {
    arr.append(i)
  }
}
print(arr)

var arr = (1...10).filter { (num) -> Bool in
  num % 2 == 1
}
print(arr)

func sum(a: String, b: String) -> String {
  return a + b
}
var result = sum(a: "你好", b:"哈哈哈")

var sumStringClosure: (String, String) -> String = {
  $0 + $1
}
sumStringClosure("hello", "world")

class Animal {
  var dog: Int?
  var cat: Int?
  init(dog: Int, cat: Int) {
    self.dog = dog
    self.cat = dog
  }
}
var daDi = Animal(dag: 2, cat: 4)
daDi.dog
daDi.cat

class Animal {
  var dog: Int?
  var cat: Int?
  init(dog: Int, cat: Int) {
    self.dog = dog
    self.cat = dog
  }
  convenience init() {
    self.init(dog: 10, cat: 10)
  }
}

var daDi = Animal()
daDi.dog
daDi.cat

var length :Double?
func getDiameter(length: Double) -> Double {
  return length * 4
}
getDiameter(length: 10)

var perimeter: Double?
var length: Double? {
willSet {
  print("准备赋值中")
}
didSet {
  perimeter = length! * 4
}
}
length = 20
perimeter

var i = 0
while i < 5 {
  print("irembeu")
  i += 1
}

for _ in 1...10 {
  print("itembeu")
}

func getDiameter(radius: Double) -> Double { return radius * 2}
func getRadius(diameter: Double) -> Double { return diameter / 2}
getDiameter(radius: 20)
getRadius(diameter: 100)

var radius: Double = 10
var diameter: Double {
  get {
    return radius * 2
    }
  set {
    radius = newValue / 2
    }
}
radius // 20
diameter // 40
diameter = 600
radius // 300

var stringArr = ["骑士", "湖人", "公牛"]
var intArr = [1, 3, 4, 5, 6]
var doubleArr = [1.0, 2.0, 3.0]
func printStringArr(a: [String]) { for s in a { print(s) } }
func printIntArr(a: [Int]) { for i in a { print(i) } }
func printDoubleArr(a: [Double]) {for d in a { print(d) } }

func printElementFromArr<T>(elements: [T]) {
  for e in elements {
    print(e)
  }
}
printElementFromArr(elements: [1,2,3,4])

func squ(x: Int) -> Int {
  return x * x
}
var s = squ(x: 10)

extension Int {
  var squ: Int {
    return self * self
  }
}
10.squ
10.squ.squ

var uName: Double?
var uPassword: Double?
func userLogIn() {
  if let username = uName {
    if let password = uPassword {
      print("欢迎, \(username)"!)
    }
  }
}

var uName: Double?
var uPassword: Double?
func userLogIn() {
   guard let username = uName, let password = uPassword 
     else { return } 
    print("欢迎, \(username)!") 
}