using System;

using System.Collections;

public class Program

{

    public static void Main()

    {   

        bool prog = false;

        var lname = new ArrayList();

        var fname = new ArrayList();

        var mname = new ArrayList();

        var un = new ArrayList();

        Console.WriteLine("Welcome! Please Register");

        Console.Write("Username: ");

        string us = Console.ReadLine();

        Console.Write("Password: ");

        string ps = Console.ReadLine();

        while (!prog) {

​

        Console.WriteLine(" ");

        Console.WriteLine("Please Log in with your Username and Password");

        Console.Write("Username: ");

        string usn = Console.ReadLine();

        Console.Write("Password: ");

        string pss = Console.ReadLine();

        if(usn.Equals(us) & pss.Equals(ps)){ 

            Console.WriteLine(" ");

            Console.WriteLine("Welcome to the Program");

            Console.WriteLine(" ");

            break;

        } else {

            Console.WriteLine(" ");

            Console.WriteLine("Incorrect");

        }

    }

        while (!prog){

        Console.WriteLine(" ");

        Console.WriteLine("What do you want to do?");

        Console.WriteLine("Please choose Between:");

        Console.WriteLine("1 = Show all Users Fullnames");

        Console.WriteLine("2 = Show all usernames");

        Console.WriteLine("3 = Add New Users Fullnames");

        Console.WriteLine("4 = Add new Users usernames");

        Console.WriteLine("5 = Remove user's username");

        Console.WriteLine("6 = End Program");

        Console.WriteLine(" ");

        int choose = Convert.ToInt32(Console.ReadLine());

            if(choose == 1) {

                Console.WriteLine(" ");

                if((lname.Count > 0) & (fname.Count > 0) & (mname.Count > 0)){

                for (int i = 0; i < lname.Count; i++){

                Console.WriteLine(lname[i] + ", " + fname[i] + ", " + mname[i]);

                } 

                } else {

                Console.WriteLine("The Fullnames' List is Empty");

                } 

            }   

                else if(choose == 2) {

                Console.WriteLine(" ");

                if(un.Count > 0){

                for (int i = 0; i < un.Count; i++){

                Console.WriteLine(un[i]);

                } 

                } else {

                Console.WriteLine("The Usernames' List is Empty");

            }

                 }

            else if(choose == 3){

                Console.WriteLine(" ");

                Console.Write("How many fullnames are you going to add?: ");

                int num = Convert.ToInt32(Console.ReadLine());

            for (int i = 0; i < num; i++) {

                Console.Write("Enter your Lastname: ");

                string ln = Console.ReadLine();

                Console.Write("Enter your Firstname: ");

                string fn = Console.ReadLine();

                Console.Write("Enter your Middlename: ");

                string mn = Console.ReadLine();

                Console.WriteLine(" ");

​

                lname.Add(ln);

                fname.Add(fn);

                mname.Add(mn);

                }

            } else if(choose == 4) {

                Console.WriteLine(" ");

                Console.Write("How many usernames are you going to add?: ");

                int num = Convert.ToInt32(Console.ReadLine());

            for (int i = 0; i < num; i++) {

                Console.WriteLine(" ");

                Console.Write("Enter Username: ");

                string usn = Console.ReadLine();

                if(un.Contains(usn)) {

                    Console.WriteLine(" ");

                    Console.WriteLine("Username is already in the list");

                    i--;

                } else {

                    un.Add(usn);

                    Console.WriteLine(" ");

                    Console.WriteLine(usn + " successfully added.");

                }

                }

            } else if(choose == 5) {

                Console.WriteLine(" ");

                Console.Write("How many usernames will be removed?: ");

                int num = Convert.ToInt32(Console.ReadLine());

                if(un.Count > num || un.Count == num) {

                    for (int i = 0; i < un.Count; i++) {

                    Console.WriteLine(un[i]);

                }

                for (int i= 0; i < num; i++) {

                Console.WriteLine(" ");

                Console.Write("Enter username to be removed: ");

                string n = Console.ReadLine();

                if(un.Contains(n)) {

                    un.Remove(n);

                    Console.WriteLine(n + " is successfully removed.");

                } else {

                    Console.WriteLine(n + " is not in the list."); 

                    i--;

                }

                }

                } else {

                    Console.WriteLine(" ");

                    Console.WriteLine("Invalid  desired number to be removed!");

            } 

            } else if (choose == 6) {

                Console.WriteLine(" ");

                Console.WriteLine("Thank you for using this program");

                prog = true;

            } else if (choose >= 7) {

                Console.WriteLine("Invalid Number! Please FOLLOW THE INSTRUCTIONS. Thank you");

            } else if (choose == 0) {

                Console.WriteLine("Invalid Number! Please FOLLOW THE INSTRUCTIONS. Thank you");

            } 

​

        }

    }

}