test2

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            while (true)
            {
                Console.WriteLine(@"{1} Convert Decimal to Binary.
                {2} Convert Decimal to Hexadecimal.
                {3} Convert Binary  to Decimal.
                {4} Convert Binary  to Hexadecimal.
                {5} Convert Hexadecimal to Decimal.
                {6} Convert Hexadecimal to Binary.
                {9} Exit." + "\r\n");

                string input = Console.ReadLine();
                int answer;
                bool checkInput = int.TryParse(input, out answer);

                if (answer == 1)
                {
                    //Convert 1234d to binary
                    Console.Write("Decimal:  ");
                    string inputDB = Console.ReadLine();
                    int decimBin;
                    bool checkinputDB = int.TryParse(inputDB, out decimBin);

                    String binN = decimalToBinary(decimBin);

                    Console.WriteLine("\r\nBinary Result:");
                    Console.WriteLine("{0}", binN.PadLeft(16, '0'));
                    Console.WriteLine("{0}", binN);
                }
            }
        }

        private static String decimalToBinary(int decimBin)
        {
            string binN = "";

            while (decimBin > 0)
            {
                int residue = decimBin % 2;
                decimBin /= 2;
                binN = residue + binN;
            }

            return binN;
        }
    }
}