Swift: Swift 输入输出与调试：print 和断点调试技巧

let scores = [85, 92, 78, 90, 88]
var total = 0
for i in 0...5 {
    total += scores[i]
}
let average = total / 5
print("平均分：\(average)")

let scores = [85, 92, 78, 90, 88]
print("数组长度：\(scores.count)")     // 输出 5
var total = 0
for i in 0..<scores.count {           // 改用 count 而非硬编码
    print("正在处理索引 \(i)：值 = \(scores[i])")
    total += scores[i]
}
print("总分：\(total)")
let average = total / 5
print("平均分：\(average)")

// 默认：空格分隔，换行结尾
print("Hello", "Swift", "World")
// Hello Swift World
// 自定义分隔符
print("Hello", "Swift", "World", separator: ", ")
// Hello, Swift, World
// 自定义结束符（不换行）
print("Loading", terminator: "...")
print("Done")
// Loading...Done
// 组合使用
print("A", "B", "C", separator: " | ", terminator: ".\n")
// A | B | C.

let name = "Alice"
let numbers = [1, 2, 3]
print(name)          // Alice
debugPrint(name)     // "Alice"
dump(name)           // - "Alice"
print(numbers)       // [1, 2, 3]
debugPrint(numbers)  // [1, 2, 3]
dump(numbers)
// - 1
// - 2
// - 3

// ============================================
// 模拟系统日志输出
// 演示 print 高级参数和 debugPrint
// ============================================
let event = "USER_LOGIN"
let user = "Alice"
let statusCode = 200
let duration = 0.045
// 1. 使用 separator 格式化日志
print("[\(event)]", user, "Status: \(statusCode)", separator: " | ", terminator: "")
print(" (\(duration)s)")
// [USER_LOGIN] | Alice | Status: 200 (0.045s)
// 2. 输出表格数据
print()
print("=== Report ===")
print("Item", "Price", "Qty", separator: " | ")
print("-----", "-----", "---", separator: " | ")
print("Book", "12.99", "3", separator: " | ")
print("Pen", "1.50", "10", separator: " | ")
print("Bag", "49.99", "1", separator: " | ")
// 3. debugPrint 用于开发调试
let input: String? = "test"
debugPrint("Debug: input = \(input)")
// "Debug: input = Optional(\"test\")"

func calculateDiscount(price: Double, percent: Double) -> Double {
    assert(price > 0, "价格必须大于 0")
    assert(percent >= 0 && percent <= 100, "折扣必须在 0-100 之间")
    let discount = price * percent / 100.0
    return price - discount
}
let finalPrice = calculateDiscount(price: 100.0, percent: 20)
print(finalPrice)  // 80.0
// 以下会在 Debug 模式下触发断言失败：
// calculateDiscount(price: -10, percent: 20)  // ❌ assert 失败
// calculateDiscount(price: 100, percent: 150) // ❌ assert 失败

func sendEmail(to address: String, message: String) {
    precondition(address.contains("@"), "无效的邮件地址：\(address)")
    precondition(!message.isEmpty, "消息不能为空")
    print("发送邮件到 \(address)：\(message)")
}
sendEmail(to: "alice@example.com", message: "Hello!")
// 发送邮件到 alice@example.com：Hello!
// 以下会触发 precondition 失败（所有模式）：
// sendEmail(to: "invalid", message: "Hi")

// ============================================
// 用户注册参数检查
// 演示 assert 和 precondition 的使用
// ============================================
import Foundation
func registerUser(name: String, age: Int, email: String) {
    // precondition：公共 API 契约（所有模式生效）
    precondition(name.count >= 2, "用户名至少 2 个字符")
    precondition(age >= 18, "用户必须年满 18 岁")
    precondition(email.contains("@"), "邮箱格式无效")
    // assert：内部逻辑检查（仅 Debug）
    let emailParts = email.split(separator: "@")
    assert(emailParts.count == 2, "邮箱应包含一个 @ 符号")
    let domain = String(emailParts[1])
    assert(domain.contains("."), "邮箱域名无效")
    // 正式注册逻辑
    print("注册成功：\(name), \(age)岁")
    print("确认邮件已发送至：\(email)")
}
// 合法调用
registerUser(name: "Alice", age: 28, email: "alice@example.com")
print("---")
// 触发 precondition 失败的调用（注释掉以避免崩溃）
// registerUser(name: "A", age: 20, email: "test@test.com")

// 在 Playground 中运行，右侧显示每步结果
let name = "Alice"    // "Alice"
var score = 0         // 0
score += 85           // 85
score += 92           // 177
let average = score / 2  // 88

func calculateTotal(items: [Double], tax: Double) -> Double {
    var subtotal = 0.0
    // 在此行设置断点
    for item in items {
        subtotal += item
    }
    let taxAmount = subtotal * tax
    let total = subtotal + taxAmount
    return total
}
let cart = [29.99, 49.99, 15.00]
let final = calculateTotal(items: cart, tax: 0.08)
print("Total: $\(final)")

// ============================================
// 练习 Playground 调试技巧
// 将此代码粘贴到 Playground 中运行
// ============================================
import Foundation
// 1. 在下面这行设置断点，观察变量值
let data: [String: Any] = [
    "product": "Swift Book",
    "price": 39.99,
    "quantity": 3,
    "inStock": true
]
// 2. 逐步执行下面的代码
let productName = data["product"] as? String ?? "Unknown"
let price = data["price"] as? Double ?? 0.0
let quantity = data["quantity"] as? Int ?? 0
let inStock = data["inStock"] as? Bool ?? false
print("Product: \(productName)")
print("Price: $\(price)")
print("Quantity: \(quantity)")
print("In Stock: \(inStock)")
// 3. 观察条件判断的结果
if inStock {
    let totalCost = price * Double(quantity)
    print("Total Cost: $\(totalCost)")
} else {
    print("Item is out of stock")
}
// 4. 使用 dump 查看复杂数据
print("\n=== Debug Info ===")
dump(data)

// ============================================
// 成绩分析工具
// 功能：print 调试 + 断言检查 + 格式化输出
// ============================================
import Foundation
// 1. 学生成绩数据
let studentName = "Alice"
let scores = [85.0, 92.0, 78.0, 90.0, 88.0]
// 2. debug 断言检查数据合法性
assert(scores.count > 0, "成绩列表不能为空")
for score in scores {
    assert(score >= 0 && score <= 100, "成绩必须在 0-100 之间：\(score)")
}
// 3. 计算统计数据
var total = 0.0
var highest = scores[0]
var lowest = scores[0]
// 添加断点观察循环过程
for (index, score) in scores.enumerated() {
    print("[DEBUG] 索引 \(index)：\(score)")
    total += score
    if score > highest { highest = score }
    if score < lowest { lowest = score }
}
let average = total / Double(scores.count)
// 4. 格式化输出结果
print(String(repeating: "=", count: 35))
print("学生：\(studentName)")
print(String(repeating: "-", count: 35))
print("成绩", "分数", "评级", separator: " | ")
print(String(repeating: "-", count: 35))
for (index, score) in scores.enumerated() {
    let grade = score >= 90 ? "A" : score >= 80 ? "B" : score >= 70 ? "C" : "D"
    print("科目\(index + 1)", score, grade, separator: " | ")
}
print(String(repeating: "-", count: 35))
print("总分：\(total)")
print("平均分：\(String(format: "%.1f", average))")
print("最高分：\(highest)")
print("最低分：\(lowest)")
print(String(repeating: "=", count: 35))
// 5. precondition 确保结果合理
precondition(average >= 0 && average <= 100, "平均分超出预期范围")
precondition(highest >= lowest, "最高分不应低于最低分")