Code

#include "stdafx.h"
#include <fstream>
#include <iostream>
#include <string>

using namespace std;

bool IsLoggedIn() {

	string username, password, pw, um;

	cout << "Enter Username : "; cin >> username;
	cout << "Enter Password : "; cin >> password;

	ifstream read("F:\\" + username + ".txt");
	getline(read, um);
	getline(read, pw);

	if (um == username && pw == password) {

		return true;
	}
	else {

		return false;
	}
}

void setUsername() {

}

void setPassword() {

}

int main() {

	int pil;

	cout << "--- Main Menu ---" << endl;
	cout << "[1] Register " << endl;
	cout << "[2] Login " << endl;
	cout << "[3] Admin Site";
	cout << "" << endl;
	cout << "Input your Chouse (1-3) : " << endl;
	cin >> pil;

	if (pil == 1) {

		string password, username;

		cout << "Input Your username : " << endl; cin >> username;
		if (username.length() > 16 || username.length() < 5) {
			cout << "Your username must be 5-16 character!" << endl;
			main();
		}
		cout << "Input your Password : " << endl; cin >> password;
		if (password.length() > 16 || password.length() < 4) {
			cout << "Your password must be 4-16 character!" << endl;
			main();
		}

		ofstream file;
		file.open("F:\\" + username + ".txt");

		file << username << endl << password;

		file.close();

		main();
	}

	else if (pil == 2) {

		bool status = IsLoggedIn();

		if (!status) {
			cout << "False Login!" << endl;
			system("PAUSE");
			return 0;
		}
		else {
			cout << "Succesfully Logged In!" << endl;
			return 1;
			main();
		}
	}
	else if (pil == 3) {

		bool status = IsLoggedIn();

		if (status == true) {
			cout << "[]-- WELCOME TO ADMIN SITE --[]" << endl;
			cout << "" << endl;
			cout << "Still Development, Comeback Later!" << endl;
			cout << "Press Esc. to back to main menu!" << endl;
		}
		else {
			cout << "- Access Denied! Unsificient permision!" << endl;

			main();
		}

	}
	main();

}