C++ code is compiling with no errors but does not give output

Question

Ok so I am trying to write a program that takes in passwords and usernames to store them in a file (I haven't written the part where they write to the file yet and will do that later), but the part of my code that reads the files causes it to not work (no output) even though it compiles with no error in VS code. To be honest, I do not completely understood what I wrote either (I just followed a youtube video), so I must be missing something about the code. For extra information I am using C++ 20 and clang++ as my compiler. I have posted my code below for reference.

#include <iostream>
#include <cstdio>
#include <vector>
#include <fstream>


using namespace::std;

class user {
    private:
        string username;
        string password;
    public:
        user(string user, string pass) {
            username = user;
            password = pass;
        }
        void SetUsername(string user) {
            username = user;
        }
        void SetPassword(string pass) {
            password = pass;
        }
        void ChangeUsername(string user) {
            username = user;
        }
        void ChangePassword(string pass) {
            password = pass;
        }
        string GetUsername() {
            return username;
        }
        string GetPassword() {
            return password;
        }
        
        

};

int main() {
    string listUsernames[1000];
    string listPasswords[1000];
    vector <user>list;
    string username;
    string password;
    string prompt;
    bool loginSuccess = false;
    bool success = false;
    int counter = 0;
    int lines = 0;

    /*
    This part is like messsing it up
    Starting from here:
    */
    ifstream file;
    file.open("usernames.txt");
    while(!file.eof()) {
        getline(file, listUsernames[lines]);
        lines++;
    }
    file.close();


    lines = 0;
    file.open("passwords.txt");
    while(!file.eof()) {
        getline(file, listPasswords[lines]);
        lines++;
    }
    file.close();

    for(int i = 0; i < lines; i++) {
        user oldUser(listUsernames[i], listPasswords[i]);
        list.push_back(oldUser);
    }
    /*
    Ending here
    */

    cout << "\tWelcome user! Please choose to login or create an account below.\n";
    do{
    cout << "\tType \"Login\" to login or \"Create\" to create a new account\n";
    cin >> prompt;
        if(prompt == "Login") {
            do{
                cout << "Username: ";
                cin >> username;
                cout << "Password: ";
                cin >> password;

                for(int i = 0; i < list.size(); i++) {
                    if(username == list[i].GetUsername() && password == list[i].GetPassword()) {
                        cout << "Hello " << list[i].GetUsername() << "!\n\n";
                        loginSuccess = true;
                        success = true;
                    }
                }
                if(!loginSuccess) {
                    cout << "Incorrect username or password";
                    counter++;
                    if(counter < 2) {
                        cout << ", please try again.\n";
                    }
                    else {
                        cout << "\nMaybe you should try creating an account! \n";
                    }
                }
            } while(!loginSuccess && counter < 2);
        }
        else if(prompt == "Create") {
            string newUsername;
            string newPassword;
            cout << "What would you like your username to be? Please enter: ";
            cin >> newUsername;
            cout << "What would you like your password to be? Please enter: ";
            cin >> newPassword;  
            user newUser(newUsername, newPassword);
            list.push_back(newUser);
            cout << "Success!\n";
            ofstream myfile;
            myfile.open("usernames");
            myfile << newUsername;
            myfile.close();
            myfile.open("passwords");
            myfile << newPassword;
            myfile.close();
        }
        else {
            cout << "Sorry, that input was not understood\n";
            cout << "Please try again\n";
        }
    } while(!success);
    return 0;
}

Answer 1

Your mistakes:

• You are writing to files "username" and "passwords" and reading from "usernames.txt" and "passwords.txt".
• You are checking while (!file.eof()) which is incorrect (link)

After fixes:

ifstream file;
file.open("usernames");
while(getline(file, listUsernames[lines])) {
    lines++;
}
file.close();


lines = 0;
file.open("passwords");
while(getline(file, listPasswords[lines])) {
    lines++;
}
file.close();

Answer 2

#include <iostream>
#include <cstdio>
#include <vector>
#include <fstream>
#include <cassert>

struct User
{
    std::string username;
    std::string password;
};

std::vector<std::string> from_file(const std::string& file_name)
{
    auto content = std::vector<std::string>{};
    auto line = std::string{};
    auto file = std::ifstream{file_name};
    while(getline(file, line)) {
        content.emplace_back(std::move(line));
    }
    return content;
}

bool login( const std::vector<User>& users )
{
    constexpr auto max_retry = 2;
    auto counter = 0U;
    while(counter < max_retry)
    {
        auto username = std::string{};
        auto password = std::string{};
        std::cout << "Username: ";
        std::cin >> username;
        std::cout << "Password: ";
        std::cin >> password;

        for(const auto& user : users) {
            if(user.username == username && user.password == password) {
                std::cout << "Hello " << username << "!\n\n";
                return true;
            }
        }

        std::cout << "Incorrect username or password";
        ++counter;
        if(counter < max_retry) {
            std::cout << ", please try again.\n";
        }
        else {
            std::cout << "\nMaybe you should try creating an account! \n";
        }
    }
    return false;
}

constexpr auto usernames_file = "usernames.txt";
constexpr auto passwords_file = "passwords.txt";

bool create(std::vector<User>& users)
{
    auto username = std::string{};
    auto password = std::string{};
    std::cout << "What would you like your username to be? Please enter: ";
    std::cin >> username;
    std::cout << "What would you like your password to be? Please enter: ";
    std::cin >> password;
    users.emplace_back(User{username, password});
    std::cout << "Success!\n";
    {
        auto file = std::ofstream{usernames_file};
        file << username;
    }
    {
        auto file = std::ofstream{passwords_file};
        file << password;
    }
    return true;
}

int main()
{
    auto list_usernames = from_file(usernames_file);
    auto list_passwords = from_file(passwords_file);

    assert(list_usernames.size() == list_passwords.size());

    auto users = std::vector<User>{};
    for(auto i = 0; i < list_usernames.size(); ++i)
    {
        users.emplace_back(User{list_usernames[i], list_passwords[i]});
    }

    std::cout << "\tWelcome user! Please choose to login or create an account below.\n";
    auto success = false;
    while(!success)
    {
        std::string prompt;
        std::cout << "\tType \"Login\" to login or \"Create\" to create a new account\n";
        std::cin >> prompt;
        if(prompt == "Login")
        {
            success = login(users);
        }
        else if(prompt == "Create")
        {
            success = create(users);
        }
        else
        {
            std::cout << "Sorry, that input was not understood\n";
            std::cout << "Please try again\n";
        }
    }
    return 0;
}