Swift 基础教程

print("Hello, Swift!")
print("Swift 是 Apple 推出的现代语言")
print("输出", 42, separator: " | ")

let name = "Swift"
var version = 5.9
version = 6.0

print("语言：\(name)")
print("版本：\(version)")

let count: Int = 42
let price: Double = 59.9
let isActive: Bool = true
let name: String = "Swift"

print("计数：\(count)，类型：\(type(of: count))")
print("价格：\(price)")
print("是否激活：\(isActive)")
print("问候：\(name) 开发者")

print("请输入一个整数：", terminator: "")
if let input = readLine(), let n = Int(input) {
    print("\(n) 的平方是 \(n * n)")
} else {
    print("输入无效")
}

let a = 17
let b = 5
print("和：\(a + b)")
print("差：\(a - b)")
print("积：\(a * b)")
print("整除商：\(a / b)")
print("余数：\(a % b)")
print("2 的 10 次方：\(pow(2.0, 10.0))")

import Foundation

let r = 7.5
let circumference = 2 * Double.pi * r
let area = Double.pi * r * r
print("周长：\(String(format: "%.4f", circumference))")
print("面积：\(String(format: "%.4f", area))")

let a = 8
let b = 12
print("a > b：\(a > b)")
print("a != b：\(a != b)")
print("a<10 && b>10：\(a < 10 && b > 10)")
print("!(a == 8)：\(!(a == 8))")

func parseNumber(_ s: String) -> Int? {
    Int(s)
}

let s1 = "42"
let s2 = "abc"

if let n = parseNumber(s1) {
    print("\(s1) 解析为 \(n)")
}

let value = parseNumber(s2) ?? -1
print("兜底值：\(value)")

func printValue(_ s: String) {
    guard let n = parseNumber(s) else {
        print("\(s) 无法解析")
        return
    }
    print("guard 解包：\(n)")
}
printValue("100")

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 day = 4
switch day {
case 1:
    print("星期一")
case 2:
    print("星期二")
case 3:
    print("星期三")
case 4:
    print("星期四")
case 5:
    print("星期五")
case 6:
    print("星期六")
case 7:
    print("星期日")
default:
    print("无效输入")
}

let score = 85
switch score {
case 90...100:
    print("优秀")
case 80..<90:
    print("良好")
case 60..<80:
    print("及格")
case 0..<60:
    print("不及格")
default:
    print("非法分数")
}

let n = 15
print(n % 2 == 0 ? "偶数" : "奇数")

let point = (3, -2)
switch point {
case (0, 0):
    print("原点")
case (_, 0):
    print("x 轴上")
case (0, _):
    print("y 轴上")
case (let x, let y) where x > 0 && y > 0:
    print("第一象限")
case (let x, let y):
    print("其它位置：(\(x), \(y))")
}

var sum = 0
for i in 1...100 {
    sum += i
}
print("1 到 100 的和：\(sum)")

for i in 1...9 {
    var row = ""
    for j in 1...i {
        row += "\(j)x\(i)=\(i * j)  "
    }
    print(row)
}

print("2 到 10 的偶数：")
for n in stride(from: 2, through: 10, by: 2) {
    print(n, terminator: " ")
}
print()

print("倒序 5 到 1：")
for n in stride(from: 5, through: 1, by: -1) {
    print(n, terminator: " ")
}
print()

for i in 1...20 {
    if i == 15 {
        break
    }
    if i % 3 != 0 {
        continue
    }
    print(i, terminator: " ")
}
print()

var sum = 0
var n = 1
while n <= 10 {
    if n % 2 == 0 {
        n += 1
        continue
    }
    sum += n
    n += 1
}
print("1..10 奇数之和：\(sum)")

var nums = [12, 45, 7, 89, 33]
nums.append(60)
nums.insert(25, at: 0)
print("大小：\(nums.count)")
print("最大值：\(nums.max()!)")
print("最小值：\(nums.min()!)")
print("排序：\(nums.sorted())")

for (index, value) in nums.enumerated() {
    print("[\(index)] = \(value)") 
}

let nums = [3, 1, 4, 1, 5, 9, 2, 6]
let doubled = nums.map { $0 * 2 }
print("翻倍：\(doubled)")

let evens = nums.filter { $0 % 2 == 0 }
print("偶数：\(evens)")

let sum = nums.reduce(0, +)
print("总和：\(sum)")

print("包含 5：\(nums.contains(5))")
print("去重：\(Set(nums).sorted())")

var ages = ["张三": 20, "李四": 22]
ages["王五"] = 24
ages["李四"] = 23
ages.removeValue(forKey: "王五")

for (name, age) in ages {
    print("\(name)：\(age) 岁")
}
print("张三年龄：\(ages["张三"] ?? 0)")
print("键列表：\(ages.keys.sorted())")

let a: Set = [1, 2, 3, 4]
let b: Set = [3, 4, 5, 6]
print("并集：\(a.union(b).sorted())")
print("交集：\(a.intersection(b).sorted())")
print("差集：\(a.subtracting(b).sorted())")

let words = ["ruby", "swift", "ruby", "kotlin", "swift"]
let unique = Set(words)
print("去重后：\(unique.sorted())")

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

func greet(name: String) -> String {
    "你好，\(name)！"
}

print("add(10, 20) = \(add(10, 20))")
print("add(3, 7) = \(add(3, 7))")
print(greet(name: "小明"))

func greet(name: String, greeting: String = "你好") -> String {
    "\(greeting)，\(name)！"
}

func sumAll(_ numbers: Int...) -> Int {
    numbers.reduce(0, +)
}

print(greet(name: "小明"))
print(greet(name: "小红", greeting: "早上好"))
print("sumAll(1,2,3,4) = \(sumAll(1, 2, 3, 4))")

let double: (Int) -> Int = { x in
    x * 2
}
print("double(5) = \(double(5))")

let nums = [1, 2, 3, 4, 5]
let doubled = nums.map { $0 * 2 }
print("map 翻倍：\(doubled)")

let evens = nums.filter { $0 % 2 == 0 }
print("filter 偶数：\(evens)")

func applyTwice(_ x: Int, op: (Int) -> Int) -> Int {
    op(op(x))
}

let inc = { (x: Int) -> Int in x + 1 }
print("applyTwice(3, +1) = \(applyTwice(3, op: inc))")

var counter = 0
let incrementCounter = {
    counter += 1
}
incrementCounter()
incrementCounter()
print("闭包捕获计数：\(counter)")

var s = "  Hello, Swift  "
s = s.trimmingCharacters(in: .whitespaces)
print("去掉空格：|\(s)|")
print("大写：\(s.uppercased())")
print("小写：\(s.lowercased())")
print("替换：\(s.replacingOccurrences(of: "Swift", with: "iOS"))")
print("字符数：\(s.count)")

let parts = s.split(separator: ",")
print("拆分：\(parts)")

import Foundation

let name = "Swift"
let total = 42
let percent = 85.5
print("语言：\(name)，版本：\(6.0)")
print("总计：\(total)，完成度：\(String(format: "%.1f%%", percent))")

let multiline = """
第一行
第二行
"""
print(multiline)

let text = "Swift Programming"
var vowelCount = 0
let vowels: Set<Character> = ["a", "e", "i", "o", "u", "A", "E", "I", "O", "U"]

for ch in text {
    if vowels.contains(ch) {
        vowelCount += 1
    }
}
print("元音字母数：\(vowelCount)")

import Foundation

let text = "swift is powerful swift is concise swift is fun"
let words = text.components(separatedBy: " ")

var freq: [String: Int] = [:]
for w in words {
    freq[w, default: 0] += 1
}

for (word, count) in freq.sorted(by: { $0.value > $1.value }) {
    print("\(word)：\(count)")
}

if let range = text.range(of: "concise") {
    let index = text.distance(from: text.startIndex, to: range.lowerBound)
    print("concise 首次出现位置：\(index)") 
}

class Student {
    var name: String
    var score: Double

    init(name: String, score: Double) {
        self.name = name
        self.score = score
    }

    func info() -> String {
        "\(name)，成绩 \(score) 分"
    }
}

let stu = Student(name: "小明", score: 92.5)
print(stu.info())

struct Point {
    var x: Double
    var y: Double

    func distance() -> Double {
        (x * x + y * y).squareRoot()
    }
}

var p1 = Point(x: 3, y: 4)
print("距离：\(p1.distance())")

var p2 = p1  // 值拷贝
p2.x = 10
print("p1.x：\(p1.x)，p2.x：\(p2.x)（互不影响）")

class Animal {
    var name: String

    init(name: String) {
        self.name = name
    }

    func speak() -> String {
        "动物叫声"
    }
}

class Dog: Animal {
    override func speak() -> String {
        "\(super.speak())：汪汪！"
    }
}

let dog = Dog(name: "旺财")
print(dog.speak())

protocol Describable {
    var description: String { get }
    func describe() -> String
}

class Document: Describable {
    var title: String

    init(title: String) {
        self.title = title
    }

    var description: String {
        "文档：\(title)"
    }

    func describe() -> String {
        "\(description)，可打印"
    }
}

let doc = Document(title: "Swift 教程")
print(doc.describe())
print("遵循协议：\(doc is Describable)")

enum ScoreError: Error {
    case outOfRange(Int)
}

func grade(_ score: Int) throws -> String {
    guard score >= 0 && score <= 100 else {
        throw ScoreError.outOfRange(score)
    }
    switch score {
    case 90...100: return "优秀"
    case 60..<90: return "及格"
    default: return "不及格"
    }
}

do {
    print(try grade(95))
    print(try grade(120))
} catch {
    print("错误：\(error)")
}

class Author {
    var name: String
    init(name: String) { self.name = name }
}

class Book {
    var title: String
    var author: Author?

    init(title: String, author: Author? = nil) {
        self.title = title
        self.author = author
    }
}

let b1 = Book(title: "Swift 教程", author: Author(name: "张三"))
let b2 = Book(title: "未署名书籍")

print("b1 作者：\(b1.author?.name ?? "未知")")
print("b2 作者：\(b2.author?.name ?? "未知")")

import Foundation

let path = "notes.txt"
let content = "第一行内容\n第二行内容"

try? content.write(toFile: path, atomically: true, encoding: .utf8)

if let read = try? String(contentsOfFile: path, encoding: .utf8) {
    print("文件内容：")
    print(read)
}

let fm = FileManager.default
print("文件存在：\(fm.fileExists(atPath: path))")

func process() {
    print("开始处理")
    defer {
        print("清理资源（最后执行）")
    }
    defer {
        print("第二个 defer（逆序先执行）")
    }
    print("处理中...")
}

process()

var total = 0
for i in 1...5 {
    total += i
}
print("闭包内作用域示例：\(total)")

func swapValues<T>(_ a: inout T, _ b: inout T) {
    let temp = a
    a = b
    b = temp
}

var x = 10
var y = 20
swapValues(&x, &y)
print("交换后：x=\(x)，y=\(y)")

var s1 = "Hello"
var s2 = "World"
swapValues(&s1, &s2)
print("字符串交换：\(s1) \(s2)")

struct Stack<T> {
    private var items: [T] = []

    mutating func push(_ item: T) {
        items.append(item)
    }

    mutating func pop() -> T? {
        items.popLast()
    }

    var isEmpty: Bool { items.isEmpty }
}

var stack = Stack<Int>()
stack.push(1)
stack.push(2)
stack.push(3)
print("出栈：\(stack.pop()!)")
print("出栈：\(stack.pop()!)")

func findMax<T: Comparable>(_ a: T, _ b: T) -> T {
    a > b ? a : b
}

print("最大：\(findMax(10, 20))")
print("最大：\(findMax(3.14, 2.71))")
print("最大：\(findMax("apple", "banana"))")

struct User: Equatable, Hashable {
    var id: Int
    var name: String
}

let u1 = User(id: 1, name: "Alice")
let u2 = User(id: 1, name: "Alice")
let u3 = User(id: 2, name: "Bob")

print("u1 == u2：\(u1 == u2)")
print("u1 == u3：\(u1 == u3)")

let users: Set<User> = [u1, u2, u3]
print("Set 去重后数量：\(users.count)")

func fetchData() async -> String {
    try? await Task.sleep(nanoseconds: 1_000_000_000)
    return "数据加载完成"
}

Task {
    let result = await fetchData()
    print(result)
}

func fetchUser() async -> String {
    try? await Task.sleep(nanoseconds: 500_000_000)
    return "用户数据"
}

func fetchPosts() async -> String {
    try? await Task.sleep(nanoseconds: 500_000_000)
    return "帖子数据"
}

Task {
    async let user = fetchUser()
    async let posts = fetchPosts()
    let result = await "用户：\(user)，帖子：\(posts)"
    print(result)
}

func download(_ name: String) async -> String {
    try? await Task.sleep(nanoseconds: 300_000_000)
    return "\(name) 下载完成"
}

Task {
    let results = await withTaskGroup(of: String.self) { group in
        for i in 1...3 {
            group.addTask {
                await download("文件\(i)")
            }
        }
        var list: [String] = []
        for await r in group {
            list.append(r)
        }
        return list
    }
    print(results)
}

import Foundation

print("开始")

DispatchQueue.global().async {
    Thread.sleep(forTimeInterval: 0.5)
    print("后台任务执行完毕")
    DispatchQueue.main.async {
        print("回到主队列更新 UI")
    }
}

RunLoop.main.run(until: Date(timeIntervalSinceNow: 1.0))

struct Student {
    let name: String
    let chinese: Double
    let math: Double

    var average: Double { (chinese + math) / 2 }
}

let students = [
    Student(name: "张三", chinese: 90, math: 85),
    Student(name: "李四", chinese: 78, math: 92),
    Student(name: "王五", chinese: 88, math: 76)
]

let sorted = students.sorted { $0.average > $1.average }
print("姓名\t语文\t数学\t平均")
for s in sorted {
    print("\(s.name)\t\(s.chinese)\t\(s.math)\t\(String(format: "%.1f", s.average))")
}

let avg = students.map(\.average).reduce(0, +) / Double(students.count)
print("全班平均：\(String(format: "%.1f", avg))")
print("第一名：\(sorted.first!.name)")

import Foundation

let text = "swift is powerful swift is concise swift is fun"
let words = text.components(separatedBy: " ")

var freq: [String: Int] = [:]
for w in words {
    freq[w, default: 0] += 1
}

let sorted = freq.sorted { $0.value > $1.value }
for (word, count) in sorted {
    print("\(word)：\(count)")
}

if let top = sorted.first {
    print("出现最多：\(top.key)，\(top.value) 次")
}

struct Todo {
    var id: Int
    var title: String
    var done: Bool = false

    mutating func toggle() {
        done.toggle()
    }
}

var todos = [
    Todo(id: 1, title: "学习 Swift 语法"),
    Todo(id: 2, title: "完成实训项目"),
    Todo(id: 3, title: "复习集合")
]

todos[1].toggle()

print("待办清单：")
for t in todos {
    let mark = t.done ? "✓" : " "
    print("[\(mark)] \(t.id). \(t.title)")
}

let pending = todos.filter { !$0.done }
print("未完成数：\(pending.count)")

import Foundation

enum CalcError: Error {
    case badFormat
    case unknownOperator(String)
    case divideByZero
}

func calculate(_ expr: String) throws -> Double {
    let parts = expr.split(separator: " ").map(String.init)
    guard parts.count == 3 else { throw CalcError.badFormat }

    guard let a = Double(parts[0]), let b = Double(parts[2]) else {
        throw CalcError.badFormat
    }

    switch parts[1] {
    case "+": return a + b
    case "-": return a - b
    case "*": return a * b
    case "/":
        guard b != 0 else { throw CalcError.divideByZero }
        return a / b
    default:
        throw CalcError.unknownOperator(parts[1])
    }
}

for expr in ["10 + 5", "10 * 3", "10 / 0", "abc + 1"] {
    do {
        print("\(expr) = \(try calculate(expr))")
    } catch {
        print("\(expr) -> 错误：\(error)")
    }
}