Code 2

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

string user;
string pass;

int LoginCheck(string user, string pass)
{
	ifstream file;
	string username, password;
	int n = 0;
	file.open("users.txt");
	if (file.is_open())
	{
		while (!file.eof())
		{
			file >> username >> password;
			n++;
			if (user == username && pass == password)
				return n;
		}
	}
	else
	{
		cout << "file not open" << endl;
	}
	return 0;
}

void Register()
{
	ifstream file;
	ofstream newuser;
	string username, password, passwordconfirm;
	file.open("users.txt", ios::app);
	newuser.open("users.txt", ios::app);
	bool uservalid = false;
	while (!uservalid)
	{
		cout << "Username: ";
		cin >> username;
		cout << "Password: ";
		cin >> password;
		cout << "Confirm password: ";
		cin >> passwordconfirm;
		int m = 0;
		int k = 0;
		while (file >> user >> pass)
		{
			m++;
			if (username != user)
				k++;
		}
		if (m == k && password == passwordconfirm)
			uservalid = true;
		else if (m != k)
			cout << "There is already a user with this username." << endl;
		else
			cout << "The passwords given do not match." << endl;
	}
	newuser << username << " " << password << endl;;
	file.close();
	newuser.close();
}

int main()
{
	int loginattempts = 0;
	ifstream userfile;
	userfile.open("users.txt");
	string userset, passset;
	if (!userfile.is_open())
	{
		cout << "file not found" << endl;
	}
	else
	{
		cout << "1.Login \n2.Register" << endl;
		int option;
		cin >> option;
		if (option == 1)
		{
			while (LoginCheck(user, pass) == 0)
			{
				loginattempts++;
				cout << "Username: ";
				cin >> user;
				cout << "Password: ";
				cin >> pass;
				if (LoginCheck(user, pass) != 0)
					cout << "Welcome " << user << "." << endl;
				else if (loginattempts == 3)
				{
					cout << "Maximum login attempts exceeded." << endl;
					break;
				}
				else
				{
					cout << "Invalid username/password combination" << endl;
				}
			}
			userfile.close();
		}
		else if (option == 2)
		{
			Register();
		}
	}
	int a;
	cin >> a; // this has no purpose other than stopping the program closing automatically
	return 0;
}