如何修复C++中‘expected primary-expression before '.' token’编译错误？

我编写了一个MKD巴士票务系统的C++代码（代码如下），目前尚未完成，但第56行持续出现expected primary-expression before '.' token编译错误。我尝试在Tickets()函数中添加newAccount变量，但问题仍未解决，请问该如何修复这个错误？

原代码 #

#include <iostream>
#include<bits/stdc++.h>

using namespace std;

struct Account {
  string username;
  string password;
};

struct Schedule{
    char place[100];
    char time[100];
};

bool validatePassword(const string& password) {
  const regex pattern("^(?=.*[A-Za-z])(?=.*\\d)(?=.*[@$!%*?&])[A-Za-z\\d@$!%*?&]{8,}$");
  return regex_match(password, pattern);
}

void createAccount() {
  Account newAccount;
  string password;

  // 获取用户名输入
  cout << "Enter Username: ";
  getline(cin, newAccount.username);

  do {
    // 获取密码输入并验证
    cout << "Enter Password (minimum 8 characters with at least 1 number and 1 special symbol): ";
    getline(cin, password);
  } while (!validatePassword(password));

  newAccount.password = password;

  // 追加模式打开文件存储账户
  ofstream outfile("accounts.txt", ios::app);

  if (outfile.is_open()) {
    outfile << newAccount.username << endl;
    outfile << newAccount.password << endl;
    outfile.close();
    cout << "Account created successfully!" << endl;
  } else {
    cerr << "Error opening file for account storage!" << endl;
  }
}

void Tickets(){
    int ticket, pw;
    
    reset:
    cout << "Enter your Password: ";
    cin >> pw;
    if (pw == Account.password){
        cout << "How many tickets will you order?: ";
        cin >> ticket;
        
        cout << "Thank you for ordering!"<<endl;
    }
    else {
        cout << "Invalid Password. Try Again!" << endl;
        goto reset;
        system ("pause");
    }
}

void Book(){
    Schedule location[100] ={   
        {"San Mateo", "5:00"},
        {"Sta. Lucia", "5:30"},
        {"Santolan", "5:35"},
        {"Cubao", "4:00"},
        {"Philcoa", "4:30"},
    };
    
    for(int i = 0; i < 6; i++){
        cout << location[i].place << endl;
    }
}
int main(){
    int choice;
    
    do{
        cout << "=== MKD Bus Ticket System ===" << endl;
        cout << "1. Create Account" << endl;
        cout << "2. Order Ticket" << endl;
        cout << "3. Book Schedule" << endl;
        cout << "4. View Schedule" << endl;
        cout << "5. Display Account" << endl;
        cout << "6. EXit" << endl;
        
        cin >> choice;
        cin.ignore();
        
        switch (choice){
        case 1:
            cout << "Account Creation screen" << endl;
            createAccount ();
            break;
        case 2:
            cout << "Order Tickets" << endl;
            Tickets ();
            break;
        case 3:
            cout << "Booking" << endl;
            Book ();
            break;
        case 4:
            cout << "Schedule Viewer" << endl;
            break;
        case 5:
            cout << "Account Information" << endl;
            break;
        case 6:
            cout << "Exit" << endl;
            break;

        }
    }while (choice != 6);
}

错误原因分析 #

第56行if (pw == Account.password)存在三个核心问题：

1. 非法访问结构体成员：Account是结构体类型，不是具体的实例对象，C++不允许直接通过类型名访问成员变量，必须通过该结构体的实例（比如currentUser.password）来访问。
2. 类型不匹配：用int类型的pw存储密码，但密码是字符串类型，不仅会导致输入截断（比如密码含非数字字符时输入失败），还无法和string类型的password正确比较。
3. 缺少用户上下文：Tickets函数没有知道当前要验证哪个用户的密码，系统没有维护登录状态，无法对应到已创建的账户。

修复方案 #

步骤1：添加登录函数，维护用户登录状态 #

新增一个login函数，读取存储的账户信息，验证用户输入的账号密码，返回登录是否成功，并传递当前登录用户的信息：

bool login(Account& currentUser) {
    string username, password;
    cout << "Enter Username: ";
    getline(cin, username);
    cout << "Enter Password: ";
    getline(cin, password);

    ifstream infile("accounts.txt");
    if (!infile.is_open()) {
        cerr << "No accounts found! Please create an account first." << endl;
        return false;
    }

    string storedUser, storedPass;
    while (getline(infile, storedUser) && getline(infile, storedPass)) {
        if (storedUser == username && storedPass == password) {
            currentUser.username = username;
            currentUser.password = password;
            cout << "Login successful!" << endl;
            infile.close();
            return true;
        }
    }
    infile.close();
    cout << "Invalid username or password!" << endl;
    return false;
}

步骤2：修改Tickets函数，接收当前登录用户信息 #

调整Tickets函数的参数，传入已登录的用户实例，同时修正密码输入的类型为string：

void Tickets(const Account& currentUser) {
    int ticket;
    string inputPw;

    reset:
    cout << "Enter your Password: ";
    getline(cin, inputPw);
    if (inputPw == currentUser.password) {
        cout << "How many tickets will you order?: ";
        cin >> ticket;
        cin.ignore(); // 清除输入缓冲区的换行符，避免后续getline出错

        cout << "Thank you for ordering!" << endl;
    } else {
        cout << "Invalid Password. Try Again!" << endl;
        goto reset;
    }
}

步骤3：更新main函数中的购票逻辑 #

在选择“订购车票”时，先执行登录验证，登录成功后再调用Tickets函数：

case 2:
    cout << "Order Tickets" << endl;
    Account currentUser;
    if (!login(currentUser)) {
        break;
    }
    Tickets(currentUser);
    break;

修复后代码说明 #

• 现在Tickets函数通过传入的currentUser实例访问密码，解决了原有的编译错误。
• 密码输入改为string类型，解决了类型不匹配问题。
• 新增的登录逻辑让系统能识别当前操作的用户，符合票务系统的基本流程。

内容的提问来源于stack exchange，提问作者johann1220