用C++开发一个简单的成绩管理系统。要求实现以下基本功能： (1）添加功能：添加学生成绩信息； （2）保存功能：保存文件并能输出学生成绩信息; （3）查询功能：1）按姓名查询成绩 2）按学号成绩 3）按科目查询成绩 4) 查询学生各科目成绩； (4）修改功能：修改学生各科目的成绩； （5）删除功能：删除学生成绩信息； （6）排序功能：按总成绩降序排列； （6）统计功能：1）统计每个学生的平均分2）统计某门课程的最高分 3）统计某课程的及格人数。 要求采用面向对象程序设计方法进行系统设计，充分应用封装、抽象 继承、多态、重载、模板等概念完成任务。 写出完整的代码

好的，以下是一个简单的成绩管理系统的完整代码：

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

const int MAX_STUDENTS = 100;

struct Score {
    float Chinese;
    float Math;
    float English;
    float Total;
};

class Student {
public:
    Student() {
        name = "";
        id = 0;
        score.Chinese = 0;
        score.Math = 0;
        score.English = 0;
        score.Total = 0;
    }
    Student(string name, int id, float chinese, float math, float english) {
        this->name = name;
        this->id = id;
        score.Chinese = chinese;
        score.Math = math;
        score.English = english;
        score.Total = chinese + math + english;
    }
    ~Student() {}
    void setName(string name) {
        this->name = name;
    }
    void setID(int id) {
        this->id = id;
    }
    void setScore(float chinese, float math, float english) {
        score.Chinese = chinese;
        score.Math = math;
        score.English = english;
        score.Total = chinese + math + english;
    }
    void deleteScore() {
        score.Chinese = 0;
        score.Math = 0;
        score.English = 0;
        score.Total = 0;
    }
    string getName() {
        return name;
    }
    int getID() {
        return id;
    }
    float getChinese() {
        return score.Chinese;
    }
    float getMath() {
        return score.Math;
    }
    float getEnglish() {
        return score.English;
    }
    float getTotal() {
        return score.Total;
    }
    bool operator==(const Student& other) {
        return (name == other.name && id == other.id);
    }
    bool operator<(const Student& other) {
        return (score.Total > other.score.Total);
    }
private:
    string name;
    int id;
    Score score;
};

class StudentManager {
public:
    StudentManager() {
        numStudents = 0;
    }
    ~StudentManager() {}
    void addStudent(Student student) {
        if (numStudents == MAX_STUDENTS) {
            cout << "Error: student list is full!" << endl;
            return;
        }
        students[numStudents] = student;
        numStudents++;
    }
    void saveToFile(string filename) {
        ofstream outfile(filename);
        if (!outfile) {
            cout << "Error: cannot open file " << filename << "!" << endl;
            return;
        }
        for (int i = 0; i < numStudents; i++) {
            outfile << students[i].getName() << " " << students[i].getID() << " "
                    << students[i].getChinese() << " " << students[i].getMath() << " "
                    << students[i].getEnglish() << " " << students[i].getTotal() << endl;
        }
        outfile.close();
    }
    Student* searchByName(string name) {
        for (int i = 0; i < numStudents; i++) {
            if (students[i].getName() == name) {
                return &students[i];
            }
        }
        return NULL;
    }
    Student* searchByID(int id) {
        for (int i = 0; i < numStudents; i++) {
            if (students[i].getID() == id) {
                return &students[i];
            }
        }
        return NULL;
    }
    Student* searchBySubject(string subject) {
        if (subject == "Chinese") {
            float maxScore = 0;
            Student* maxStudent = NULL;
            for (int i = 0; i < numStudents; i++) {
                if (students[i].getChinese() > maxScore) {
                    maxScore = students[i].getChinese();
                    maxStudent = &students[i];
                }
            }
            return maxStudent;
        }
        else if (subject == "Math") {
            float maxScore = 0;
            Student* maxStudent = NULL;
            for (int i = 0; i < numStudents; i++) {
                if (students[i].getMath() > maxScore) {
                    maxScore = students[i].getMath();
                    maxStudent = &students[i];
                }
            }
            return maxStudent;
        }
        else if (subject == "English") {
            float maxScore = 0;
            Student* maxStudent = NULL;
            for (int i = 0; i < numStudents; i++) {
                if (students[i].getEnglish() > maxScore) {
                    maxScore = students[i].getEnglish();
                    maxStudent = &students[i];
                }
            }
            return maxStudent;
        }
        else {
            return NULL;
        }
    }
    Score* searchScores(Student student) {
        return &(student.score);
    }
    void modifyScore(Student* student, float chinese, float math, float english) {
        student->setScore(chinese, math, english);
    }
    void deleteStudent(Student* student) {
        for (int i = 0; i < numStudents; i++) {
            if (students[i] == *student) {
                for (int j = i; j < numStudents - 1; j++) {
                    students[j] = students[j + 1];
                }
                numStudents--;
                break;
            }
        }
    }
    float calculateAverageScore(Student student) {
        return student.getTotal() / 3;
    }
    float calculateMaxScore(string subject) {
        float maxScore = 0;
        for (int i = 0; i < numStudents; i++) {
            if (subject == "Chinese" && students[i].getChinese() > maxScore) {
                maxScore = students[i].getChinese();
            }
            else if (subject == "Math" && students[i].getMath() > maxScore) {
                maxScore = students[i].getMath();
            }
            else if (subject == "English" && students[i].getEnglish() > maxScore) {
                maxScore = students[i].getEnglish();
            }
        }
        return maxScore;
    }
    int calculatePassNum(string subject) {
        int numPass = 0;
        for (int i = 0; i < numStudents; i++) {
            if (subject == "Chinese" && students[i].getChinese() >= 60) {
                numPass++;
            }
            else if (subject == "Math" && students[i].getMath() >= 60) {
                numPass++;
            }
            else if (subject == "English" && students[i].getEnglish() >= 60) {
                numPass++;
            }
        }
        return numPass;
    }
    void sortStudents() {
        for (int i = 0; i < numStudents - 1; i++) {
            for (int j = i + 1; j < numStudents; j++) {
                if (students[i] < students[j]) {
                    Student temp = students[i];
                    students[i] = students[j];
                    students[j] = temp;
                }
            }
        }
    }
private:
    Student students[MAX_STUDENTS];
    int numStudents;
};

int main() {
    StudentManager sm;
    int choice = 0;
    while (true) {
        cout << "Please choose an operation:" << endl;
        cout << "1. Add student" << endl;
        cout << "2. Save to file" << endl;
        cout << "3. Search by name" << endl;
        cout << "4. Search by ID" << endl;
        cout << "5. Search by subject" << endl;
        cout << "6. Search scores" << endl;
        cout << "7. Modify score" << endl;
        cout << "8. Delete student" << endl;
        cout << "9. Calculate average score" << endl;
        cout << "10. Calculate max score" << endl;
        cout << "11. Calculate pass num" << endl;
        cout << "12. Sort students" << endl;
        cout << "0. Exit" << endl;
        cin >> choice;
        if (choice == 0) {
            break;
        }
        else if (choice == 1) {
            string name;
            int id;
            float chinese, math, english;
            cout << "Please enter student name: ";
            cin >> name;
            cout << "Please enter student ID: ";
            cin >> id;
            cout << "Please enter Chinese score: ";
            cin >> chinese;
            cout << "Please enter Math score: ";
            cin >> math;
            cout << "Please enter English score: ";
            cin >> english;
            Student student(name, id, chinese, math, english);
            sm.addStudent(student);
            cout << "Added student:" << endl;
            cout << "Name: " << name << endl;
            cout << "ID: " << id << endl;
            cout << "Chinese score: " << chinese << endl;
            cout << "Math score: " << math << endl;
            cout << "English score: " << english << endl;
        }
        else if (choice == 2) {
            string filename;
            cout << "Please enter filename: ";
            cin >> filename;
            sm.saveToFile(filename);
            cout << "Saved to file " << filename << "!" << endl;
        }
        else if (choice == 3) {
            string name;
            cout << "Please enter student name: ";
            cin >> name;
            Student* student = sm.searchByName(name);
            if (student == NULL) {
                cout << "Cannot find student " << name << "!" << endl;
            }
            else {
                cout << "Name: " << student->getName() << endl;
                cout << "ID: " << student->getID() << endl;
                cout << "Chinese score: " << student->getChinese() << endl;
                cout << "Math score: " << student->getMath() << endl;
                cout << "English score: " << student->getEnglish() << endl;
                cout << "Total score: " << student->getTotal() << endl;
            }
        }
        else if (choice == 4) {
            int id;
            cout << "Please enter student ID: ";
            cin >> id;
            Student* student = sm.searchByID(id);
            if (student == NULL) {
                cout << "Cannot find student with ID " << id << "!" << endl;
            }
            else {
                cout << "Name: " << student->getName() << endl;
                cout << "ID: " << student->getID() << endl;
                cout << "Chinese score: " << student->getChinese() << endl;
                cout << "Math score: " << student->getMath() << endl;
                cout << "English score: " << student->getEnglish() << endl;
                cout << "Total score: " << student->getTotal() << endl;
            }
        }
        else if (choice == 5) {
            string subject;
            cout << "Please enter subject (Chinese, Math, English): ";
            cin >> subject;
            Student* student = sm.searchBySubject(subject);
            if (student == NULL) {
                cout << "Cannot find max score of subject " << subject << "!" << endl;
            }
            else {
                cout << "Name: " << student->getName() << endl;
                cout << "ID: " << student->getID() << endl;
                cout << subject << " score: " << student->getChinese() << endl;
            }
        }
        else if (choice == 6) {
            string name;
            int id;
            cout << "Please enter student name: ";
            cin >> name;
            cout << "Please enter student ID: ";
            cin >> id;
            Student* student = sm.searchByName(name);
            if (student == NULL || student->getID() != id) {
                cout << "Cannot find student " << name << " with ID " << id << "!" << endl;
            }
            else {
                Score* score = sm.searchScores(*student);
                cout << "Name: " << student->getName() << endl;
                cout << "ID: " << student->getID() << endl;
                cout << "Chinese score: " << score->Chinese << endl;
                cout << "Math score: " << score->Math << endl;
                cout << "English score: " << score->English << endl;
                cout << "Total score: " << score->Total << endl;
            }
        }
        else if (choice == 7) {