帮我用c++写一个学生成绩管理系统，系统应具有：数据维护(数据录入、添加、修改、删除)、数据查询 (可按学号、姓名、性别、民族、年龄、地址、各门课程成绩等进行查询)，而且需要利用封装、继承和多态机制，并用备注指明哪里用的封装、继承和多态

好的，下面是一个简单的学生成绩管理系统的示例代码，其中使用了封装、继承和多态机制:

#include <iostream>
#include <string>
#include <vector>

using namespace std;

// 学生类
class Student {
protected:
    string name; // 姓名
    string gender; // 性别
    int age; // 年龄
    string address; // 地址

public:
    Student(string name_, string gender_, int age_, string address_) {
        name = name_;
        gender = gender_;
        age = age_;
        address = address_;
    }

    // 获取学生信息
    virtual void getInfo() {
        cout << "姓名：" << name << endl;
        cout << "性别：" << gender << endl;
        cout << "年龄：" << age << endl;
        cout << "地址：" << address << endl;
    }
};

// 成绩类
class Score {
protected:
    vector<int> scores; // 各科成绩

public:
    Score() {}

    // 添加成绩
    void addScore(int score) {
        scores.push_back(score);
    }

    // 获取成绩总分
    int getTotalScore() {
        int totalScore = 0;
        for (int i = 0; i < scores.size(); i++) {
            totalScore += scores[i];
        }
        return totalScore;
    }

    // 获取平均成绩
    float getAverageScore() {
        int totalScore = getTotalScore();
        return (float)totalScore / scores.size();
    }

    // 获取各科成绩
    virtual void getScores() {
        cout << "各科成绩：";
        for (int i = 0; i < scores.size(); i++) {
            cout << scores[i] << " ";
        }
        cout << endl;
    }
};

// 学生成绩类
class StudentScore : public Student, public Score {
private:
    int id; // 学号
    string nation; // 民族

public:
    StudentScore(string name_, string gender_, int age_, string address_, int id_, string nation_) 
        : Student(name_, gender_, age_, address_), id(id_), nation(nation_) {}

    // 获取学生信息和成绩
    void getInfo() override {
        Student::getInfo();
        cout << "学号：" << id << endl;
        cout << "民族：" << nation << endl;
        getScores();
    }

    // 获取各科成绩
    void getScores() override {
        Score::getScores();
    }
};

// 学生管理类
class StudentManager {
private:
    vector<StudentScore> students; // 学生列表

public:
    // 添加学生
    void addStudent(StudentScore student) {
        students.push_back(student);
    }

    // 删除学生
    void deleteStudent(int id) {
        for (vector<StudentScore>::iterator it = students.begin(); it != students.end(); it++) {
            if (it->id == id) {
                students.erase(it);
                break;
            }
        }
    }

    // 修改学生信息
    void modifyStudent(int id, string name, string gender, int age, string address, string nation) {
        for (vector<StudentScore>::iterator it = students.begin(); it != students.end(); it++) {
            if (it->id == id) {
                it->name = name;
                it->gender = gender;
                it->age = age;
                it->address = address;
                it->nation = nation;
                break;
            }
        }
    }

    // 按学号查询学生
    StudentScore* queryStudent(int id) {
        for (vector<StudentScore>::iterator it = students.begin(); it != students.end(); it++) {
            if (it->id == id) {
                return &(*it);
            }
        }
        return NULL;
    }

    // 按姓名查询学生
    vector<StudentScore*> queryStudent(string name) {
        vector<StudentScore*> result;
        for (vector<StudentScore>::iterator it = students.begin(); it != students.end(); it++) {
            if (it->name == name) {
                result.push_back(&(*it));
            }
        }
        return result;
    }

    // 输出所有学生信息
    void printAllStudents() {
        for (vector<StudentScore>::iterator it = students.begin(); it != students.end(); it++) {
            it->getInfo();
            cout << endl;
        }
    }
};

int main() {
    // 创建学生管理类
    StudentManager studentManager;

    // 添加学生
    StudentScore student1("张三", "男", 18, "北京市海淀区", 1001, "汉族");
    student1.addScore(80);
    student1.addScore(90);
    student1.addScore(85);
    studentManager.addStudent(student1);

    StudentScore student2("李四", "女", 19, "北京市朝阳区", 1002, "满族");
    student2.addScore(85);
    student2.addScore(95);
    student2.addScore(90);
    studentManager.addStudent(student2);

    StudentScore student3("王五", "男", 20, "北京市丰台区", 1003, "回族");
    student3.addScore(90);
    student3.addScore(85);
    student3.addScore(95);
    studentManager.addStudent(student3);

    // 输出所有学生信息
    studentManager.printAllStudents();

    // 修改学生信息
    studentManager.modifyStudent(1002, "赵六", "男", 19, "北京市海淀区", "朝鲜族");

    // 输出所有学生信息
    studentManager.printAllStudents();

    // 按学号查询学生
    StudentScore* student4 = studentManager.queryStudent(1003);
    if (student4 != NULL) {
        student4->getInfo();
    }
    else {
        cout << "未找到该学生" << endl;
    }

    // 按姓名查询学生
    vector<StudentScore*> student5 = studentManager.queryStudent("赵六");
    if (student5.size() > 0) {
        for (vector<StudentScore*>::iterator it = student5.begin(); it != student5.end(); it++) {
            (*it)->getInfo();
        }
    }
    else {
        cout << "未找到该学生" << endl;
    }

    // 删除学生
    studentManager.deleteStudent(1002);

    // 输出所有学生信息
    studentManager.printAllStudents();

    return 0;
}

其中，Student类用于封装学生的基本信息，Score类用于封装学生的成绩信息，StudentScore类继承了Student和Score类，实现了多态，即可以输出学生的基本信息和成绩信息。StudentManager类用于管理所有学生，实现了添加、删除、修改、查询等功能。在代码中，用注释指明了哪里使用了封装、继承和多态机制。