用c++编程开发一个学生选课管理系统，数据用mysql保存

好的，以下是一个简单的学生选课管理系统的示例代码。需要注意的是，这只是一个基本框架，具体的实现细节需要根据具体情况进行调整和完善。

首先，需要安装并配置好MySQL C++ Connector，才能连接数据库。然后，我们需要定义一个Course类和Student类，用来存储课程和学生的信息。接下来是代码实现：

#include <iostream>
#include <string>
#include <vector>
#include <mysql_connection.h>
#include <mysql_driver.h>
#include <cppconn/prepared_statement.h>
#include <cppconn/resultset.h>

using namespace std;
using namespace sql;

class Course {
public:
    int id;
    string name;
    int credit;
    int capacity;
    int enrolled;
};

class Student {
public:
    int id;
    string name;
    vector<int> courses;
};

int main() {
    // Connect to MySQL database
    Driver* driver = get_driver_instance();
    Connection* conn = driver->connect("tcp://127.0.0.1:3306", "root", "password");
    conn->setSchema("course_selection");

    // Load courses from database
    vector<Course> courses;
    PreparedStatement* stmt = conn->prepareStatement("SELECT * FROM courses");
    ResultSet* res = stmt->executeQuery();
    while (res->next()) {
        Course course;
        course.id = res->getInt("id");
        course.name = res->getString("name");
        course.credit = res->getInt("credit");
        course.capacity = res->getInt("capacity");
        course.enrolled = res->getInt("enrolled");
        courses.push_back(course);
    }
    delete res;
    delete stmt;

    // Load students from database
    vector<Student> students;
    stmt = conn->prepareStatement("SELECT * FROM students");
    res = stmt->executeQuery();
    while (res->next()) {
        Student student;
        student.id = res->getInt("id");
        student.name = res->getString("name");
        string courses_str = res->getString("courses");
        size_t pos = 0;
        while ((pos = courses_str.find(",")) != string::npos) {
            int course_id = stoi(courses_str.substr(0, pos));
            student.courses.push_back(course_id);
            courses[course_id].enrolled++;
            courses_str.erase(0, pos + 1);
        }
        int course_id = stoi(courses_str);
        student.courses.push_back(course_id);
        courses[course_id].enrolled++;
        students.push_back(student);
    }
    delete res;
    delete stmt;

    // Main loop
    while (true) {
        cout << "1. View courses" << endl;
        cout << "2. View students" << endl;
        cout << "3. Enroll student" << endl;
        cout << "4. Drop student" << endl;
        cout << "5. Exit" << endl;
        cout << "Enter your choice: ";
        int choice;
        cin >> choice;
        switch (choice) {
        case 1:
            // View courses
            cout << "ID\tName\tCredit\tCapacity\tEnrolled" << endl;
            for (const Course& course : courses) {
                cout << course.id << "\t" << course.name << "\t" << course.credit << "\t"
                     << course.capacity << "\t" << course.enrolled << endl;
            }
            break;
        case 2:
            // View students
            cout << "ID\tName\tCourses" << endl;
            for (const Student& student : students) {
                cout << student.id << "\t" << student.name << "\t";
                for (int course_id : student.courses) {
                    cout << courses[course_id].name << " ";
                }
                cout << endl;
            }
            break;
        case 3:
            // Enroll student
            cout << "Enter student ID: ";
            int student_id;
            cin >> student_id;
            cout << "Enter course ID: ";
            int course_id;
            cin >> course_id;
            if (students[student_id].courses.size() >= 3) {
                cout << "You have already enrolled in 3 courses." << endl;
            } else if (courses[course_id].enrolled >= courses[course_id].capacity) {
                cout << "This course is full." << endl;
            } else {
                students[student_id].courses.push_back(course_id);
                courses[course_id].enrolled++;
                PreparedStatement* stmt = conn->prepareStatement("UPDATE students SET courses=? WHERE id=?");
                string courses_str;
                for (int course_id : students[student_id].courses) {
                    courses_str += to_string(course_id) + ",";
                }
                courses_str.pop_back();
                stmt->setString(1, courses_str);
                stmt->setInt(2, student_id);
                stmt->executeUpdate();
                delete stmt;
                stmt = conn->prepareStatement("UPDATE courses SET enrolled=? WHERE id=?");
                stmt->setInt(1, courses[course_id].enrolled);
                stmt->setInt(2, course_id);
                stmt->executeUpdate();
                delete stmt;
                cout << "Enrolled successfully." << endl;
            }
            break;
        case 4:
            // Drop student
            cout << "Enter student ID: ";
            cin >> student_id;
            cout << "Enter course ID: ";
            cin >> course_id;
            bool found = false;
            for (int i = 0; i < students[student_id].courses.size(); i++) {
                if (students[student_id].courses[i] == course_id) {
                    students[student_id].courses.erase(students[student_id].courses.begin() + i);
                    courses[course_id].enrolled--;
                    PreparedStatement* stmt = conn->prepareStatement("UPDATE students SET courses=? WHERE id=?");
                    string courses_str;
                    for (int course_id : students[student_id].courses) {
                        courses_str += to_string(course_id) + ",";
                    }
                    courses_str.pop_back();
                    stmt->setString(1, courses_str);
                    stmt->setInt(2, student_id);
                    stmt->executeUpdate();
                    delete stmt;
                    stmt = conn->prepareStatement("UPDATE courses SET enrolled=? WHERE id=?");
                    stmt->setInt(1, courses[course_id].enrolled);
                    stmt->setInt(2, course_id);
                    stmt->executeUpdate();
                    delete stmt;
                    cout << "Dropped successfully." << endl;
                    found = true;
                    break;
                }
            }
            if (!found) {
                cout << "You are not enrolled in this course." << endl;
            }
            break;
        case 5:
            // Exit
            conn->close();
            exit(0);
        default:
            cout << "Invalid choice." << endl;
            break;
        }
    }

    return 0;
}

在上面的代码中，我们首先连接到MySQL数据库，然后从courses表和students表中读取信息，存储到相应的Course和Student对象中。然后，在主循环中，我们提供了一些选项，让用户可以查看课程和学生的信息，以及进行选课和退课操作。每次修改后，我们需要更新数据库中的数据。

需要注意的是，这里假设students表中的courses字段是用逗号分隔的字符串，例如"1,2,3"表示该学生已经选了ID为1、2、3的三门课。如果您的数据结构不同，需要对代码进行相应的修改。