C++ 入门教程（七）：结构体与枚举

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Student s = {"小明", 18, 90.5};
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Student* p = &s;
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std::cout << (*p).name << "\n";    // 括号版（* 优先级低于 .）
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std::cout << p->name << "\n";      // 箭头版（完全等价，推荐）
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p->score = 95;                     // 通过指针修改成员

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// 大结构体只读：const& 零拷贝
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void print_student(const Student& s) {
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    std::cout << s.name << "," << s.age << "岁," << s.score << "分\n";
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}
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// 要修改：引用
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void birthday(Student& s) {
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    ++s.age;
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}
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// 值传递会整体拷贝（string/vector 都复制一遍）——大结构体别这么传

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struct Point {
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    double x, y;
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    // 成员函数（第九篇正式讲）
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    double dist() const { return std::sqrt(x*x + y*y); }
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};

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enum Color { RED, GREEN, BLUE };        // 默认值 0,1,2
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Color c = GREEN;
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std::cout << c << "\n";                 // 1（本质是 int）
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if (c == GREEN) std::cout << "绿色\n";
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enum Level { LOW, MID = 5, HIGH };      // 可指定值：0,5,6

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enum TrafficLight { RED, YELLOW, GREEN };   // ❌ RED/GREEN 与 Color 重复定义！

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enum class Status { Idle, Running, Error };
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enum class Color2 { Red, Green };          // 同名不冲突：有作用域
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Status s = Status::Running;                 // 必须带作用域 Status::
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if (s == Status::Running)
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    std::cout << "运行中\n";
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// int n = s;               // ❌ 不隐式转 int（类型安全）
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int n = static_cast<int>(s); // 显式转换 ✓
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// 指定底层类型
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enum class Priority : char { Low = 'L', Mid = 'M', High = 'H' };

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enum class OrderState { Created, Paid, Shipped, Done, Cancelled };
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void handle(OrderState state) {
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    switch (state) {
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        case OrderState::Created:  std::cout << "待支付\n"; break;
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        case OrderState::Paid:     std::cout << "已支付，备货中\n"; break;
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        case OrderState::Shipped:  std::cout << "运输中\n"; break;
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        case OrderState::Done:     std::cout << "已完成\n"; break;
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        case OrderState::Cancelled:std::cout << "已取消\n"; break;
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        // ⚠ 开了 -Wall 编译选项时，漏分支会警告——enum+switch 的安全网
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    }
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}