int main() { User currentUser("", "", 0.0); while (true) { // 显示菜单 cout << "1. Register" << endl; cout << "

可以将这段代码写为类`User`的一个公共的菜单函数，如下所示： ```c++ class User { private: string username; string password; double balance; bool loggedIn; public: User(string username, string password, double balance) { this->username = username; this->password = password; this->balance = balance; this->loggedIn = false; } // 省略其他成员函数 void menu() { while (true) { // 显示菜单 cout << "1. Register" << endl; cout << "2. Login" << endl; cout << "3. Logout" << endl; cout << "4. Exit" << endl; // 获取用户选择 int choice; cin >> choice; switch (choice) { case 1: registerUser(); break; case 2: if (!loggedIn) { loginUser(*this); } else { cout << "You are already logged in." << endl; } break; case 3: if (loggedIn) { logout(); cout << "Logout successful!" << endl; } else { cout << "You are not logged in." << endl; } break; case 4: return; default: cout << "Invalid choice." << endl; break; } } } }; ``` 在这个版本中，我们将菜单循环封装到了`User`类的`menu()`函数中。在菜单循环中，我们使用了当前对象的成员变量和成员函数，而不是传递参数。这样，我们就可以通过创建`User`对象并调用其`menu()`函数来启动菜单循环了。