帮我用c++写一个程序：学生成绩管理系统，并实现以下要求： 定义学生（student）类，其中包括姓名、性别、学号、班级和语文数学英语物理学科的成绩。 设计菜单实现功能选择； 输入功能：输入学生信息，并以txt格式保存到文件中； 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。 能根据学号修改学生信息； 能根据学号删除学生信息； 查询功能： 能够根据学号查询学生信息； 能够根据姓名、班级查询学生信息； 统计学生成绩，按照班级和科目计算平均分。 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。

好的，下面是我给您实现的代码，希望能满足您的需求：

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;

class Student {
public:
    string name, gender, id, cls;
    int chinese, math, english, physics;
    int totalScore;
    double avgScore;
    Student(string _name, string _gender, string _id, string _cls, int _chinese, int _math, int _english, int _physics) {
        name = _name;
        gender = _gender;
        id = _id;
        cls = _cls;
        chinese = _chinese;
        math = _math;
        english = _english;
        physics = _physics;
        totalScore = chinese + math + english + physics;
        avgScore = totalScore / 4.0;
    }
};

vector<Student> students;

void addStudent() {
    string name, gender, id, cls;
    int chinese, math, english, physics;
    cout << "请输入学生姓名：";
    cin >> name;
    cout << "请输入学生性别：";
    cin >> gender;
    cout << "请输入学生学号：";
    cin >> id;
    cout << "请输入学生班级：";
    cin >> cls;
    cout << "请输入学生语文成绩：";
    cin >> chinese;
    cout << "请输入学生数学成绩：";
    cin >> math;
    cout << "请输入学生英语成绩：";
    cin >> english;
    cout << "请输入学生物理成绩：";
    cin >> physics;
    students.push_back(Student(name, gender, id, cls, chinese, math, english, physics));
    ofstream outfile;
    outfile.open("students.txt", ios::app);
    outfile << name << " " << gender << " " << id << " " << cls << " " << chinese << " " << math << " " << english << " " << physics << endl;
    outfile.close();
}

void readStudentData() {
    ifstream infile;
    infile.open("students.txt");
    if (!infile) {
        cout << "文件不存在" << endl;
        return;
    }
    while (!infile.eof()) {
        string name, gender, id, cls;
        int chinese, math, english, physics;
        infile >> name >> gender >> id >> cls >> chinese >> math >> english >> physics;
        students.push_back(Student(name, gender, id, cls, chinese, math, english, physics));
    }
    infile.close();
}

void saveStudentData() {
    ofstream outfile;
    outfile.open("students.txt", ios::trunc);
    for (int i = 0; i < students.size(); ++i) {
        outfile << students[i].name << " " << students[i].gender << " " << students[i].id << " " << students[i].cls << " " << students[i].chinese << " " << students[i].math << " " << students[i].english << " " << students[i].physics << endl;
    }
    outfile.close();
}

void printStudents() {
    cout << "姓名\t性别\t学号\t班级\t语文\t数学\t英语\t物理\t总分\t平均分" << endl;
    for (int i = 0; i < students.size(); ++i) {
        cout << students[i].name << "\t" << students[i].gender << "\t" << students[i].id << "\t" << students[i].cls << "\t" << students[i].chinese << "\t" << students[i].math << "\t" << students[i].english << "\t" << students[i].physics << "\t" << students[i].totalScore << "\t" << students[i].avgScore << endl;
    }
}

bool compareChinese(Student a, Student b) {
    return a.chinese > b.chinese;
}

bool compareMath(Student a, Student b) {
    return a.math > b.math;
}

bool compareEnglish(Student a, Student b) {
    return a.english > b.english;
}

bool comparePhysics(Student a, Student b) {
    return a.physics > b.physics;
}

bool compareTotalScore(Student a, Student b) {
    return a.totalScore > b.totalScore;
}

void sortByName() {
    sort(students.begin(), students.end(), [](Student a, Student b) { return a.name < b.name; });
    printStudents();
}

void sortByChinese() {
    sort(students.begin(), students.end(), compareChinese);
    printStudents();
}

void sortByMath() {
    sort(students.begin(), students.end(), compareMath);
    printStudents();
}

void sortByEnglish() {
    sort(students.begin(), students.end(), compareEnglish);
    printStudents();
}

void sortByPhysics() {
    sort(students.begin(), students.end(), comparePhysics);
    printStudents();
}

void sortByTotalScore() {
    sort(students.begin(), students.end(), compareTotalScore);
    printStudents();
}

void modifyStudent() {
    string id;
    cout << "请输入要修改信息的学生的学号：";
    cin >> id;
    bool found = false;
    for (int i = 0; i < students.size(); ++i) {
        if (students[i].id == id) {
            cout << "请输入学生姓名：";
            cin >> students[i].name;
            cout << "请输入学生性别：";
            cin >> students[i].gender;
            cout << "请输入学生学号：";
            cin >> students[i].id;
            cout << "请输入学生班级：";
            cin >> students[i].cls;
            cout << "请输入学生语文成绩：";
            cin >> students[i].chinese;
            cout << "请输入学生数学成绩：";
            cin >> students[i].math;
            cout << "请输入学生英语成绩：";
            cin >> students[i].english;
            cout << "请输入学生物理成绩：";
            cin >> students[i].physics;
            students[i].totalScore = students[i].chinese + students[i].math + students[i].english + students[i].physics;
            students[i].avgScore = students[i].totalScore / 4.0;
            found = true;
            break;
        }
    }
    if (!found) {
        cout << "未找到该学生" << endl;
        return;
    }
    saveStudentData();
    cout << "修改成功" << endl;
}

void deleteStudent() {
    string id;
    cout << "请输入要删除信息的学生的学号：";
    cin >> id;
    bool found = false;
    for (int i = 0; i < students.size(); ++i) {
        if (students[i].id == id) {
            students.erase(students.begin() + i);
            found = true;
            break;
        }
    }
    if (!found) {
        cout << "未找到该学生" << endl;
        return;
    }
    saveStudentData();
    cout << "删除成功" << endl;
}

void searchById() {
    string id;
    cout << "请输入要查询信息的学生的学号：";
    cin >> id;
    bool found = false;
    for (int i = 0; i < students.size(); ++i) {
        if (students[i].id == id) {
            cout << "姓名\t性别\t学号\t班级\t语文\t数学\t英语\t物理\t总分\t平均分" << endl;
            cout << students[i].name << "\t" << students[i].gender << "\t" << students[i].id << "\t" << students[i].cls << "\t" << students[i].chinese << "\t" << students[i].math << "\t" << students[i].english << "\t" << students[i].physics << "\t" << students[i].totalScore << "\t" << students[i].avgScore << endl;
            found = true;
            break;
        }
    }
    if (!found) {
        cout << "未找到该学生" << endl;
        return;
    }
}

void searchByNameOrCls() {
    string nameOrCls;
    cout << "请输入要查询信息的学生的姓名或班级：";
    cin >> nameOrCls;
    bool found = false;
    for (int i = 0; i < students.size(); ++i) {
        if (students[i].name == nameOrCls || students[i].cls == nameOrCls) {
            cout << "姓名\t性别\t学号\t班级\t语文\t数学\t英语\t物理\t总分\t平均分" << endl;
            cout << students[i].name << "\t" << students[i].gender << "\t" << students[i].id << "\t" << students[i].cls << "\t" << students[i].chinese << "\t" << students[i].math << "\t" << students[i].english << "\t" << students[i].physics << "\t" << students[i].totalScore << "\t" << students[i].avgScore << endl;
            found = true;
        }
    }
    if (!found) {
        cout << "未找到该学生" << endl;
        return;
    }
}

void calculateAvgScoreByClsAndSubject() {
    string cls;
    int chineseSum = 0, mathSum = 0, englishSum = 0, physicsSum = 0;
    double chineseAvg = 0.0, mathAvg = 0.0, englishAvg = 0.0, physicsAvg = 0.0;
    int chineseCount = 0, mathCount = 0, englishCount = 0, physicsCount = 0;
    cout << "请输入要统计的班级：";
    cin >> cls;
    for (int i = 0; i < students.size(); ++i) {
        if (students[i].cls == cls) {
            chineseSum += students[i].chinese;
            mathSum += students[i].math;
            englishSum += students[i].english;
            physicsSum += students[i].physics;
            chineseCount++;
            mathCount++;
            englishCount++;
            physicsCount++;
        }
    }
    chineseAvg = chineseSum / (double)chineseCount;
    mathAvg = mathSum / (double)mathCount;
    englishAvg = englishSum / (double)englishCount;
    physicsAvg = physicsSum / (double)physicsCount;
    cout << "班级：" << cls << endl;
    cout << "语文平均分：" << chineseAvg << endl;
    cout << "数学平均分：" << mathAvg << endl;
    cout << "英语平均分：" << englishAvg << endl;
    cout << "物理平均分：" << physicsAvg << endl;
}

int main() {
    readStudentData();
    while (true) {
        cout << "------------------------" << endl;
        cout << "1.添加学生信息" << endl;
        cout << "2.计算每个学生的总分与平均分" << endl;
        cout << "3.按照学生的每一科的功课成绩和总分的成绩排序" << endl;
        cout << "4.根据学号修改学生信息" << endl;
        cout << "5.根据学号删除学生信息" << endl;
        cout << "6.根据学号查询学生信息" << endl;
        cout << "7.根据姓名、班级查询学生信息" << endl;
        cout << "8.统计学生成绩，按照班级和科目计算平均分" << endl;
        cout << "9.退出系统" << endl;
        cout << "------------------------" << endl;
        int choice;
        cout << "请输入选项：";
        cin >> choice;
        switch (choice) {
            case 1:
                addStudent();
                break;
            case 2:
                printStudents();
                break;
            case 3:
                int sortChoice;
                cout << "1.按照语文成绩排序" << endl;
                cout << "2.按照数学成绩排序" << endl;
                cout << "3.按照英语成绩排序" << endl;
                cout << "4.按照物理成绩排序" << endl;
                cout << "5.按照总分排序" << endl;
                cout << "请输入选项：";
                cin >> sortChoice;
                switch (sortChoice) {
                    case 1:
                        sortByChinese();
                        break;
                    case 2:
                        sortByMath();
                        break;
                    case 3:
                        sortByEnglish();
                        break;
                    case 4:
                        sortByPhysics();
                        break;
                    case 5:
                        sortByTotalScore();
                        break;
                    default:
                        cout << "无效选项" << endl;
                        break;
                }
                break;
            case 4:
                modifyStudent();
                break;
            case 5:
                deleteStudent();
                break;
            case 6:
                searchById();
                break;
            case 7:
                searchByNameOrCls();
                break;
            case 8:
                calculateAvgScoreByClsAndSubject();
                break;
            case 9:
                return 0;
            default:
                cout << "无效选项" << endl;
                break;
        }
    }
    return 0;
}

程序中使用了一个 vector 来存储学生信息，通过读写文件实现了数据的持久化。在实现各种功能时，可以看到程序使用了 C++11 中引入的 lambda 表达式来简化排序操作，提高了代码的可读性和简洁性。