I'm currently working on my final project of my first semester of C++ (and programming in general). What my professor wants us to do is to make a mock social media program that has some basic functions such as:Sign upSign inFollow userWrite a postView Activity  (Activity from friends)View Profile  (Username, followers, people you follow, posts from you)Sign OutExitOn the prompt it says that he:expects to see knowledge of the material, in particular Object Oriented Design - Classes.I assume that means that we should be using classes properly.That brings me to my general question about the code I have, which is whether or not I'm fulfilling that requirement of demonstrating knowledge of using classes (or objects or whatever he's probably expecting).project02.cpp#include <iostream>#include <fstream>#include <string>#include <cstdlib>#include project02.husing namespace std;ofstream fout;ifstream fin;void LoginScreen(){    cout << Please select from the following options by entering the corresponding number: << endl << endl;    cout << 1. Sign up << endl;    cout << 2. Log in << endl;    cout << 3. User list << endl;    cout << 4. Exit << endl << endl;    cout << Please make your selection (enter 1, 2, 3, or 4): ;}void UserInfo::signUp(){    int offset;    string line;    bool isTaken;    string fName;    string lName;    string bYear;    string screenName;    cout << Enter your first name: ;    cin >> fName;    setFirstName(fName);    cout << Enter your last name: ;    cin >> lName;    setLastName(lName);    cout << Enter your birth year: ;    cin >> bYear;    setBirthYear(bYear);    cout << Create your screen name (no special characters or spaces): ;    do    {        cin >> screenName;        isTaken = false;        fin.open(RegisteredUsers.txt);        while (!fin.eof())        {            getline(fin, line);            if ((offset = line.find(screenName, 0)) != string::npos)            {                isTaken = true;                cout << The username  << screenName <<  is already taken, please choose a different username: ;            }        }        fin.close();    } while (isTaken = true && isTaken != false);    setScreenName(screenName);    cout << endl;    cout << Registered with the following information: << endl;    cout << endl;    cout << Full name:  << getFirstName() <<   << getLastName() << endl;    cout << Birth year:  << getBirthYear() << endl;    cout << Screen name:  << getScreenName() << endl;    cout << You may now log in to your newly created account. << endl;    cout << endl;    string infoFileName = screenName + _info.txt;    string followerFileName = screenName + _follow.txt;    string activityFileName = screenName + _activity.txt;    registerUser(fout, screenName);    fout.open(infoFileName.c_str());    writeUserInfo(fout, fName, lName, bYear, screenName);    fout.close();}void writeUserInfo(ofstream & fout, string & first, string & last, string & year, string & screen){    fout << first +   + last +   + year +   + screen +  ;}void registerUser(ofstream & fout, string screen){    fout.open(RegisteredUsers.txt, ios::app);    fout <<   + screen;    fout.close();}void listUsers(){    ifstream fin;    string screen;    cout << The following users are registered:  << endl << endl;    fin.open(RegisteredUsers.txt);    while(!fin.eof())    {        fin >> screen;        cout << screen << endl;    }    fin.close();}void UserInfo::signIn(){    int offset;    string line;    bool exists;    string screenName;    cout << Please enter your screen name to sign in: ;    do    {        cin >> screenName;        exists = true;            fin.open(RegisteredUsers.txt);            while (!fin.eof())            {                getline(fin, line);                if ((offset = line.find(screenName, 0)) == string::npos)                {                    exists = false;                    cout << endl;                    cout << User  << screenName <<  does not exist! << endl << endl;                    cout << Please enter an existing username to sign in: ;                }            }            fin.close();    } while (exists = false || exists != true);    cout << You are now logged in as  + screenName << endl;}void UserInfo::displayProfile(){}void UserInfo::setFirstName(string fName){    _firstName = fName;}string UserInfo::getFirstName(){    return _firstName;}void UserInfo::setLastName(string lName){    _lastName = lName;}string UserInfo::getLastName(){    return _lastName;}void UserInfo::setBirthYear(string bYear){    _birthYear = bYear;}string UserInfo::getBirthYear(){    return _birthYear;}void UserInfo::setScreenName(string screenName){    _screenName = screenName;}string UserInfo::getScreenName(){    return _screenName;}project02.h#ifndef PROJECT02_H#define PROJECT02_Husing namespace std;void LoginScreen();void writeUserInfo(ofstream & fout, string & first, string & last, string & year, string & screen);void registerUser(ofstream & fout, string screen);void listUsers();class UserInfo{    public:        string getFirstName();        void setFirstName(string first);        string getLastName();        void setLastName(string last);        string getBirthYear();        void setBirthYear(string year);        string getScreenName();        void setScreenName(string sn);        void signUp();        void signIn();        void displayProfile();    private:        string _firstName;        string _lastName;        string _birthYear;        string _screenName;};#endif // PROJECT02_Hproject02main.cpp#include <iostream>#include <fstream>#include <string>#include <cstdlib>#include project02.husing namespace std;int main(){    char input;    UserInfo inputInfo;    cout << Welcome to MyFace, a social media network where you can post your thoughts and see what your friends are up to. << endl << endl;    do    {        LoginScreen();        cin >> input;        cout << endl;        if (input == '1' && input != '2' && input != '3')        {            inputInfo.signUp();        }        else if (input == '2' && input != '3')        {            inputInfo.signIn();        }        else if(input == '3')        {            listUsers();            cout << endl;            system(PAUSE);            cout << endl;            LoginScreen();        }        else if (input != '1' && input != '2' && input != '3' && input != '4')        {            cout << Invalid choice! Redirecting to login page... << endl << endl;        }        else if (input == '4')        {            cout << Thank you for using MyFace. << endl;        }    } while (input != '4');    return 0;}As you can see, it doesn't yet include all the functionalities and signIn() doesn't actually do anything yet as that's where I left off. Anyway, I'm still just a beginner but please let me know if you see any potential problems or if I'm not using classes properly, or if you just have any general comments!I don't actually have a whole lot of time to finish this so if something doesn't NEED to be fixed then I probably won't want to fix it, especially if it involves heavy restructuring or is otherwise time consuming.
C++ mock social networking program
c++;beginner