用c++定义学生中小学生，中学生，大学生三个

以下是使用C++定义学生类别的示例代码：

#include <iostream>
#include <string>

// 基类：学生
class Student {
protected:
    std::string name;
    int age;

public:
    Student(std::string name, int age) : name(name), age(age) {}

    virtual void display() {
        std::cout << "Name: " << name << std::endl;
        std::cout << "Age: " << age << std::endl;
    }
};

// 小学生类
class ElementaryStudent : public Student {
private:
    int grade;

public:
    ElementaryStudent(std::string name, int age, int grade) : Student(name, age), grade(grade) {}

    void display() override {
        std::cout << "Elementary Student" << std::endl;
        Student::display();
        std::cout << "Grade: " << grade << std::endl;
    }
};

// 中学生类
class MiddleSchoolStudent : public Student {
private:
    int grade;

public:
    MiddleSchoolStudent(std::string name, int age, int grade) : Student(name, age), grade(grade) {}

    void display() override {
        std::cout << "Middle School Student" << std::endl;
        Student::display();
        std::cout << "Grade: " << grade << std::endl;
    }
};

// 大学生类
class CollegeStudent : public Student {
private:
    std::string major;

public:
    CollegeStudent(std::string name, int age, std::string major) : Student(name, age), major(major) {}

    void display() override {
        std::cout << "College Student" << std::endl;
        Student::display();
        std::cout << "Major: " << major << std::endl;
    }
};

int main() {
    Student* student1 = new ElementaryStudent("John", 8, 3);
    student1->display();

    std::cout << std::endl;

    Student* student2 = new MiddleSchoolStudent("Alice", 14, 9);
    student2->display();

    std::cout << std::endl;

    Student* student3 = new CollegeStudent("Bob", 20, "Computer Science");
    student3->display();

    delete student1;
    delete student2;
    delete student3;

    return 0;
}

这段代码定义了一个基类`Student`，以及三个派生类`ElementaryStudent`（小学生）、`MiddleSchoolStudent`（中学生）和`CollegeStudent`（大学生）。每个类都有自己的特定属性和方法，并且它们都重写了基类的`display()`方法以显示相应的信息。在主函数中，创建了几个不同类型的学生对象，并调用它们的`display()`方法以展示各自的信息。最后，记得释放动态分配的内存。