main.cpp

#include<iostream>
#include<istream>
#include<fstream>
#include<string.h>
#include <map>
#include <limits>
using namespace std;

//Declare user's choice validation function.
int validateChoice();

class User {
    //Declare variables and users map.
    string username, password, firstname, lastname, city;
    map<string, string> users = {};

public:
    void login();
    void signUp();
    void seeUsers();
};

int main() {

    User user;
    int choice;

    //As long as the user does not quit by pressing 4, keep going.
    do {
        //Get user's menu selection.
        cout << "1. Login " << endl << "2. Sign Up " << endl << "3. See Users " << endl << "4. Quit " << endl;
        cout << "CHOOSE FROM THE SELECTION MENU (enter a number to go): " << endl;
        choice = validateChoice();

        switch (choice) {

            case 1:
                user.login();
                break;

            case 2:
                user.signUp();
                break;

            case 3:
                user.seeUsers();
                break;

            case 4:
                cout << "GoodBye!" << endl;
                break;

            default:
                break;

        }

    } while (choice != 4);

    return 0;
}
void User::login() {

    //Get username and password.
    cout << "Username (NO SPACES):";
    cin >> username;
    cout << "Password: ";
    cin >> password;

    //Check if the username exists in the map or not.
    if (users.count(username) != 0) {

        //If it exists, then compare the password that was entered.
        if (users[username] == password) {
            cout << "Logged In SUCCESSFUL \n WELCOME! " << endl;
            cout <<"YOUR DETAILS ARE:\n" << endl;
            cout <<"First Name: " << firstname<<endl;
            cout <<"Last Name: " << lastname <<endl;
            cout <<"CITY: " << city << endl;
            cout <<"USERNAME: " << username<<endl;
            cout <<"Password: " << password <<endl;
            int answer;
            cout <<"DO YOU WISH TO EDIT YOUR INFORMATION? PLEASE TYPE 1 FOR YES and 0 FOR NO: ";
            cin >> answer;
            if (answer==1)
            {
                cout << "First Name: ";
                cin >> firstname;
                cout << "Last Name: ";
                cin >> lastname;
                cout << "City: ";
                cin >> city;
                cout << "Username(NO SPACES): ";
                cin >> username;
                cout << "Password: ";
                cin >> password;

                //Check if that username is already taken or not.
                if (users.count(username) == 0) {
                    //If the username was not taken, sign the user up.
                    users.insert({username, password});
                    cout << "Your details have been updated! " << endl;
                } 
                else {
                    //If the username was taken, display appropriate message.
                    cout << "Username already taken " << endl;
                }
            }
            else
            {
                cout<<"THank YOU !" <<endl;
            }  
        }
        else {
            cout << "Wrong password! " << endl;
        }

    } else {
        //If the username did not exist, prompt the user to sign up.
        cout << "Sign up First! " << endl;
    }

}
void User::signUp() {

    //Get username and password.
    cout << "First Name: ";
    cin >> firstname;
    cout << "Last Name: ";
    cin >> lastname;
    cout << "City: ";
    cin >> city;
    cout << "Username(NO SPACES): ";
    cin >> username;
    cout << "Password: ";
    cin >> password;

    //Check if that username is already taken or not.
    if (users.count(username) == 0) {

        //If the username was not taken, sign the user up.
        users.insert({username, password});
        cout << "Signed up! " << endl;
    } else {
        //If the username was taken, display appropriate message.
        cout << "Username already taken " << endl;
    }

}

//Display the usernames of all the signed up users.
void User::seeUsers() {

    //Check to see if the map is empty.
    if (!users.empty()) {

        //If map is not empty, display the usernames of the users.
        cout << "Usernames: " << endl;
        for (auto it = users.cbegin(); it != users.cend(); it++) {
            cout << it->first <<  endl;
        }

    } else {

        //If map is empty, show the appropriate message.
        cout << "There are no users to display! " << endl;

    }

}

//Validate user's menu selection.
int validateChoice() {
    int retVal;

    //Input has to be numeric.
    while (!(cin >> retVal)) {
        cout << "Enter numeric values 1 - 4: ";
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
    }

    //Input has to be between 1 and 4.
    if (retVal < 1 || retVal > 4) {
        cout << "Enter numeric values 1 - 4: ";
        retVal = validateChoice();
    }

    return retVal;
}