用C++设计一个学生管理系统要求250行代码

以下是一个简单的C++学生管理系统示例代码，包含了学生类的定义、学生信息的输入、输出、查询和修改等基本功能，共计约250行代码：

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

using namespace std;

// 学生类定义
class Student {
public:
    string id; // 学号
    string name; // 姓名
    int age; // 年龄
    char gender; // 性别
    vector<double> scores; // 成绩
    double average; // 平均成绩

    // 构造函数
    Student(string id = "", string name = "", int age = 0, char gender = 'M') {
        this->id = id;
        this->name = name;
        this->age = age;
        this->gender = gender;
        this->scores.clear();
        this->average = 0;
    }

    // 计算平均成绩
    void calcAverage() {
        double sum = 0;
        for (int i = 0; i < scores.size(); i++) {
            sum += scores[i];
        }
        average = sum / scores.size();
    }

    // 显示学生信息
    void display() {
        cout << "ID: " << id << endl;
        cout << "Name: " << name << endl;
        cout << "Age: " << age << endl;
        cout << "Gender: " << gender << endl;
        cout << "Scores: ";
        for (int i = 0; i < scores.size(); i++) {
            cout << scores[i] << " ";
        }
        cout << endl;
        cout << "Average: " << average << endl;
    }
};

// 学生管理系统类定义
class StudentManager {
private:
    vector<Student> students; // 学生列表

public:
    // 添加学生
    void addStudent() {
        string id, name;
        int age;
        char gender;
        cout << "Please input student ID: ";
        cin >> id;
        cout << "Please input student name: ";
        cin >> name;
        cout << "Please input student age: ";
        cin >> age;
        cout << "Please input student gender (M/F): ";
        cin >> gender;
        Student student(id, name, age, gender);
        students.push_back(student);
        cout << "Add student successfully." << endl;
    }

    // 显示所有学生信息
    void displayAll() {
        for (int i = 0; i < students.size(); i++) {
            students[i].display();
        }
    }

    // 按学号查询学生信息
    void queryById() {
        string id;
        cout << "Please input student ID: ";
        cin >> id;
        for (int i = 0; i < students.size(); i++) {
            if (students[i].id == id) {
                students[i].display();
                return;
            }
        }
        cout << "Student not found." << endl;
    }

    // 修改学生信息
    void modify() {
        string id;
        cout << "Please input student ID: ";
        cin >> id;
        for (int i = 0; i < students.size(); i++) {
            if (students[i].id == id) {
                cout << "Please input new name (old name: " << students[i].name << "): ";
                cin >> students[i].name;
                cout << "Please input new age (old age: " << students[i].age << "): ";
                cin >> students[i].age;
                cout << "Please input new gender (old gender: " << students[i].gender << "): ";
                cin >> students[i].gender;
                cout << "Please input new scores (old scores: ";
                for (int j = 0; j < students[i].scores.size(); j++) {
                    cout << students[i].scores[j] << " ";
                }
                cout << "): ";
                students[i].scores.clear();
                double score;
                while (cin >> score) {
                    students[i].scores.push_back(score);
                }
                students[i].calcAverage();
                cout << "Modify student successfully." << endl;
                return;
            }
        }
        cout << "Student not found." << endl;
    }

    // 保存学生信息到文件
    void saveToFile() {
        ofstream fout("students.txt");
        for (int i = 0; i < students.size(); i++) {
            fout << students[i].id << " " << students[i].name << " " << students[i].age << " " << students[i].gender << " ";
            for (int j = 0; j < students[i].scores.size(); j++) {
                fout << students[i].scores[j] << " ";
            }
            fout << endl;
        }
        fout.close();
        cout << "Save students to file successfully." << endl;
    }

    // 从文件中读取学生信息
    void readFromFile() {
        ifstream fin("students.txt");
        if (fin) {
            students.clear();
            string line;
            while (getline(fin, line)) {
                istringstream iss(line);
                string id, name;
                int age;
                char gender;
                iss >> id >> name >> age >> gender;
                Student student(id, name, age, gender);
                double score;
                while (iss >> score) {
                    student.scores.push_back(score);
                }
                student.calcAverage();
                students.push_back(student);
            }
            fin.close();
            cout << "Read students from file successfully." << endl;
        } else {
            cout << "Cannot open file students.txt." << endl;
        }
    }
};

// 主函数
int main() {
    StudentManager manager;
    int op;
    do {
        cout << "Please choose operation:" << endl;
        cout << "1. Add student" << endl;
        cout << "2. Display all students" << endl;
        cout << "3. Query by ID" << endl;
        cout << "4. Modify student" << endl;
        cout << "5. Save students to file" << endl;
        cout << "6. Read students from file" << endl;
        cout << "0. Exit" << endl;
        cin >> op;
        switch (op) {
        case 1:
            manager.addStudent();
            break;
        case 2:
            manager.displayAll();
            break;
        case 3:
            manager.queryById();
            break;
        case 4:
            manager.modify();
            break;
        case 5:
            manager.saveToFile();
            break;
        case 6:
            manager.readFromFile();
            break;
        case 0:
            cout << "Goodbye!" << endl;
            break;
        default:
            cout << "Invalid operation." << endl;
            break;
        }
    } while (op != 0);
    return 0;
}

注意：这只是一个简单的示例代码，可能还有很多功能和优化可以加入。