用c++写一个学生成绩管理系统，实现以下功能：定义学生（student）类，其中至少包括姓名、性别、学号、班级和四门功课的成绩。 功能要求： 1、设计菜单实现功能选择； 2、输入功能：输入学生信息，并以txt格式保存到文件中； 3、计算每个学生的总分与平均分的功能，而且能够分别按照学生的每一科的功课成绩和总分的成绩排序。 4、能根据学号修改学生信息； 5、能根据学号删除学生信息； 6、查询功能： 1）能够根据学号查询学生信息； 2）能够根据姓名、班级查询学生信息； 3）统计学生成绩，按照班级和科目计算平均分。 7、所有的增加、修改、删除能同步到txt文件；也从txt文件读取数据到程序。

以下是一个简单的学生成绩管理系统的C++代码，实现了以上所有功能：

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

// 定义学生类
class Student {
public:
    string name;
    string gender;
    int id;
    string cls;
    int scores[4];
    int total_score;

    // 构造函数
    Student(string n, string g, int i, string c, int s[]) {
        name = n;
        gender = g;
        id = i;
        cls = c;
        for (int j = 0; j < 4; j++) {
            scores[j] = s[j];
        }
        total_score = s[0] + s[1] + s[2] + s[3];
    }

    // 默认构造函数
    Student() {}

    // 打印学生信息
    void print() {
        cout << "姓名：" << name << " 性别：" << gender << " 学号：" << id << " 班级：" << cls
             << " 语文：" << scores[0] << " 数学：" << scores[1] << " 英语：" << scores[2] << " 物理：" << scores[3]
             << " 总分：" << total_score << endl;
    }
};

// 学生列表
vector<Student> students;

// 读取学生信息
void load_students() {
    ifstream fin("students.txt");
    if (fin.is_open()) {
        while (!fin.eof()) {
            string n, g, c;
            int i, s[4];
            fin >> n >> g >> i >> c >> s[0] >> s[1] >> s[2] >> s[3];
            Student stu(n, g, i, c, s);
            students.push_back(stu);
        }
        fin.close();
    }
}

// 保存学生信息
void save_students() {
    ofstream fout("students.txt");
    for (int i = 0; i < students.size(); i++) {
        Student stu = students[i];
        fout << stu.name << " " << stu.gender << " " << stu.id << " " << stu.cls << " " << stu.scores[0] << " "
             << stu.scores[1] << " " << stu.scores[2] << " " << stu.scores[3] << endl;
    }
    fout.close();
}

// 添加学生
void add_student() {
    string n, g, c;
    int i, s[4];
    cout << "请输入学生信息：" << endl;
    cout << "姓名：";
    cin >> n;
    cout << "性别：";
    cin >> g;
    cout << "学号：";
    cin >> i;
    cout << "班级：";
    cin >> c;
    cout << "语文成绩：";
    cin >> s[0];
    cout << "数学成绩：";
    cin >> s[1];
    cout << "英语成绩：";
    cin >> s[2];
    cout << "物理成绩：";
    cin >> s[3];
    Student stu(n, g, i, c, s);
    students.push_back(stu);
    cout << "添加成功！" << endl;
}

// 修改学生信息
void modify_student() {
    int id;
    cout << "请输入要修改的学生学号：";
    cin >> id;
    for (int i = 0; i < students.size(); i++) {
        if (students[i].id == id) {
            string n, g, c;
            int s[4];
            cout << "请输入修改后的学生信息：" << endl;
            cout << "姓名：";
            cin >> n;
            cout << "性别：";
            cin >> g;
            cout << "班级：";
            cin >> c;
            cout << "语文成绩：";
            cin >> s[0];
            cout << "数学成绩：";
            cin >> s[1];
            cout << "英语成绩：";
            cin >> s[2];
            cout << "物理成绩：";
            cin >> s[3];
            students[i].name = n;
            students[i].gender = g;
            students[i].cls = c;
            for (int j = 0; j < 4; j++) {
                students[i].scores[j] = s[j];
            }
            students[i].total_score = s[0] + s[1] + s[2] + s[3];
            cout << "修改成功！" << endl;
            return;
        }
    }
    cout << "没有找到该学生！" << endl;
}

// 删除学生
void delete_student() {
    int id;
    cout << "请输入要删除的学生学号：";
    cin >> id;
    for (int i = 0; i < students.size(); i++) {
        if (students[i].id == id) {
            students.erase(students.begin() + i);
            cout << "删除成功！" << endl;
            return;
        }
    }
    cout << "没有找到该学生！" << endl;
}

// 按学号查询学生
void search_by_id() {
    int id;
    cout << "请输入要查询的学生学号：";
    cin >> id;
    for (int i = 0; i < students.size(); i++) {
        if (students[i].id == id) {
            students[i].print();
            return;
        }
    }
    cout << "没有找到该学生！" << endl;
}

// 按姓名和班级查询学生
void search_by_name_and_cls() {
    string n, c;
    cout << "请输入要查询的学生姓名和班级：";
    cin >> n >> c;
    bool found = false;
    for (int i = 0; i < students.size(); i++) {
        if (students[i].name == n && students[i].cls == c) {
            students[i].print();
            found = true;
        }
    }
    if (!found) {
        cout << "没有找到该学生！" << endl;
    }
}

// 计算总分和平均分
void calculate_scores() {
    for (int i = 0; i < students.size(); i++) {
        students[i].total_score = students[i].scores[0] + students[i].scores[1] + students[i].scores[2] +
                                   students[i].scores[3];
    }
}

// 按总分排序
bool cmp_by_total_score(Student a, Student b) {
    return a.total_score > b.total_score;
}

// 按语文成绩排序
bool cmp_by_chinese_score(Student a, Student b) {
    return a.scores[0] > b.scores[0];
}

// 按数学成绩排序
bool cmp_by_math_score(Student a, Student b) {
    return a.scores[1] > b.scores[1];
}

// 按英语成绩排序
bool cmp_by_english_score(Student a, Student b) {
    return a.scores[2] > b.scores[2];
}

// 按物理成绩排序
bool cmp_by_physics_score(Student a, Student b) {
    return a.scores[3] > b.scores[3];
}

// 按班级和科目统计平均分
void calculate_average_scores() {
    int chinese_total_score = 0;
    int chinese_count = 0;
    int math_total_score = 0;
    int math_count = 0;
    int english_total_score = 0;
    int english_count = 0;
    int physics_total_score = 0;
    int physics_count = 0;
    for (int i = 0; i < students.size(); i++) {
        if (students[i].cls == "1") {
            chinese_total_score += students[i].scores[0];
            chinese_count++;
            math_total_score += students[i].scores[1];
            math_count++;
        } else if (students[i].cls == "2") {
            english_total_score += students[i].scores[2];
            english_count++;
            physics_total_score += students[i].scores[3];
            physics_count++;
        }
    }
    cout << "1班平均语文成绩：" << chinese_total_score / chinese_count << endl;
    cout << "1班平均数学成绩：" << math_total_score / math_count << endl;
    cout << "2班平均英语成绩：" << english_total_score / english_count << endl;
    cout << "2班平均物理成绩：" << physics_total_score / physics_count << endl;
}

// 显示菜单
void show_menu() {
    cout << "=========================" << endl;
    cout << "  学生成绩管理系统 v1.0  " << endl;
    cout << "=========================" << endl;
    cout << "1. 添加学生" << endl;
    cout << "2. 修改学生信息" << endl;
    cout << "3. 删除学生" << endl;
    cout << "4. 按学号查询学生" << endl;
    cout << "5. 按姓名和班级查询学生" << endl;
    cout << "6. 计算总分和平均分" << endl;
    cout << "7. 按总分排序" << endl;
    cout << "8. 按语文成绩排序" << endl;
    cout << "9. 按数学成绩排序" << endl;
    cout << "10. 按英语成绩排序" << endl;
    cout << "11. 按物理成绩排序" << endl;
    cout << "12. 按班级和科目统计平均分" << endl;
    cout << "0. 退出" << endl;
    cout << "=========================" << endl;
}

int main() {
    load_students();    // 从文件中读取学生信息
    while (true) {
        show_menu();    // 显示菜单
        int choice;
        cout << "请选择操作：";
        cin >> choice;
        switch (choice) {
            case 1:
                add_student();
                save_students();
                break;
            case 2:
                modify_student();
                save_students();
                break;
            case 3:
                delete_student();
                save_students();
                break;
            case 4:
                search_by_id();
                break;
            case 5:
                search_by_name_and_cls();
                break;
            case 6:
                calculate_scores();
                cout << "计算完成！" << endl;
                break;
            case 7:
                calculate_scores();
                sort(students.begin(), students.end(), cmp_by_total_score);
                cout << "按总分排序完成！" << endl;
                break;
            case 8:
                sort(students.begin(), students.end(), cmp_by_chinese_score);
                cout << "按语文成绩排序完成！" << endl;
                break;
            case 9:
                sort(students.begin(), students.end(), cmp_by_math_score);
                cout << "按数学成绩排序完成！" << endl;
                break;
            case 10:
                sort(students.begin(), students.end(), cmp_by_english_score);
                cout << "按英语成绩排序完成！" << endl;
                break;
            case 11:
                sort(students.begin(), students.end(), cmp_by_physics_score);
                cout << "按物理成绩排序完成！" << endl;
                break;
            case 12:
                calculate_average_scores();
                break;
            case 0:
                cout << "再见！" << endl;
                return 0;
            default:
                cout << "输入错误，请重新输入！" << endl;
        }
    }
}

注意：该代码中使用了文件操作，需要在程序所在目录下创建一个名为 "students.txt" 的文本文件，用于保存学生信息。