条件语句 #

let score = 85

if score >= 60 {
    print("及格")
}

let score = 55

if score >= 60 {
    print("及格")
} else {
    print("不及格")
}

let score = 85

if score >= 90 {
    print("优秀")
} else if score >= 80 {
    print("良好")
} else if score >= 60 {
    print("及格")
} else {
    print("不及格")
}

let age = 25
let hasID = true

if age >= 18 && hasID {
    print("可以进入")
}

let name: String? = "张三"

if let unwrappedName = name {
    print("名字是: \(unwrappedName)")
}

let firstName: String? = "张"
let lastName: String? = "三"

if let first = firstName, let last = lastName {
    print("全名: \(first)\(last)")
}

let age: Int? = 25

if let unwrappedAge = age, unwrappedAge >= 18 {
    print("成年人，年龄: \(unwrappedAge)")
}

let number = 2

switch number {
case 1:
    print("一")
case 2:
    print("二")
case 3:
    print("三")
default:
    print("其他")
}

let char: Character = "a"

switch char {
case "a", "e", "i", "o", "u":
    print("元音")
default:
    print("辅音")
}

let score = 85

switch score {
case 0..<60:
    print("不及格")
case 60..<80:
    print("及格")
case 80..<90:
    print("良好")
case 90...100:
    print("优秀")
default:
    print("无效分数")
}

let point = (1, 1)

switch point {
case (0, 0):
    print("原点")
case (_, 0):
    print("在x轴上")
case (0, _):
    print("在y轴上")
case (-2...2, -2...2):
    print("在范围内")
default:
    print("在范围外")
}

let point = (2, 3)

switch point {
case (let x, 0):
    print("在x轴上，x = \(x)")
case (0, let y):
    print("在y轴上，y = \(y)")
case let (x, y):
    print("坐标: (\(x), \(y))")
}

let point = (3, 4)

switch point {
case let (x, y) where x == y:
    print("在对角线上")
case let (x, y) where x == -y:
    print("在反对角线上")
case let (x, y):
    print("坐标: (\(x), \(y))")
}

let number = 2

switch number {
case 1:
    print("一")
    fallthrough
case 2:
    print("二")
    fallthrough
case 3:
    print("三")
default:
    print("其他")
}

let number = 2

switch number {
case 1:
    print("一")
case 2:
    print("二")
    fallthrough
case 3:
    print("三")
default:
    print("其他")
}

let score = 75
let result = score >= 60 ? "及格" : "不及格"
print(result)

let score = 85
let grade = score >= 90 ? "A" : score >= 80 ? "B" : score >= 60 ? "C" : "D"
print(grade)

let isLoggedIn = true
let buttonTitle = isLoggedIn ? "退出" : "登录"
print(buttonTitle)

let name: String? = nil
let displayName = name ?? "匿名"
print(displayName)

let nickname: String? = nil
let username: String? = nil
let defaultName = "匿名"

let displayName = nickname ?? username ?? defaultName
print(displayName)

enum Direction {
    case north, south, east, west
}

let direction = Direction.north

switch direction {
case .north:
    print("向北")
case .south:
    print("向南")
case .east:
    print("向东")
case .west:
    print("向西")
}

let numbers: [Int?] = [1, 2, nil, 4, nil, 6]

for case let number? in numbers {
    print(number)
}

let value: Any = "Hello"

switch value {
case is Int:
    print("是整数")
case is String:
    print("是字符串")
case is Double:
    print("是浮点数")
default:
    print("未知类型")
}

func calculate(_ a: Double, _ op: String, _ b: Double) -> Double? {
    switch op {
    case "+":
        return a + b
    case "-":
        return a - b
    case "*":
        return a * b
    case "/":
        return b != 0 ? a / b : nil
    default:
        return nil
    }
}

if let result = calculate(10, "+", 5) {
    print("结果: \(result)")
}

enum State {
    case idle
    case loading
    case success(String)
    case error(String)
}

let state = State.success("数据加载完成")

switch state {
case .idle:
    print("空闲")
case .loading:
    print("加载中...")
case .success(let message):
    print("成功: \(message)")
case .error(let message):
    print("错误: \(message)")
}

func validateInput(_ input: String?) -> String {
    guard let input = input, !input.isEmpty else {
        return "输入不能为空"
    }
    
    guard input.count >= 3 else {
        return "输入长度至少3个字符"
    }
    
    guard input.count <= 20 else {
        return "输入长度不能超过20个字符"
    }
    
    return "输入有效"
}

print(validateInput(nil))
print(validateInput(""))
print(validateInput("ab"))
print(validateInput("valid input"))

func process(name: String?, age: Int?) {
    guard let name = name, !name.isEmpty else {
        print("名字无效")
        return
    }
    
    guard let age = age, age >= 0 else {
        print("年龄无效")
        return
    }
    
    print("处理: \(name), \(age)岁")
}

let number = 2

switch number {
case 1:
    print("一")
case 2:
    print("二")
default:
    break
}

func checkUser(user: User?) {
    guard let user = user else {
        return
    }
    
    guard user.isActive else {
        return
    }
    
    guard user.hasPermission else {
        return
    }
    
    print("用户验证通过")
}