Display in words the numerical value

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace tryingstartfror4digits
{
class Program
{
    static void Main(string[] args)
    {
        Program pg=new Program();
        Console.WriteLine("Enter ur number");
        int num = Convert.ToInt32(Console.ReadLine());
        if (num <= 19)
        {
            string g = pg.first(num);
            Console.WriteLine("The number is " + g);
        }
        else if ((num >= 20) && (num <= 99))
        {
                if (num % 10 == 0)
                {
                    string g = pg.second(num / 10);
                    Console.WriteLine("The number is " + g);
                }
                else
                {
                    string g = pg.second(num / 10) + pg.first(num % 10);
                    Console.WriteLine("The number is " + g);
                }
          }
        else if((num>=100) && (num<=999))
        {
            int k = num % 100;
            string g = pg.first(num / 100) +pg.third(0) + pg.second(k / 10)+pg.first(k%10);
            Console.WriteLine("The number is " + g);
          }
        else if ((num >= 1000) && (num <= 19999))
        {
            int h=num%1000;
           int k=h%100;
            string g = pg.first(num / 1000) + "Thousand " + pg.first(h/ 100) + pg.third(k) + pg.second(k / 10) + pg.first(k % 10);
            Console.WriteLine("The number is " + g);
        }
        Console.ReadLine();
    }
     public string first(int num)
    {
        string name;
        if (num == 0)
        {
            name = " ";
        }
        else
        {
            string[] arr1 = new string[] { "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine" , "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
            name = arr1[num - 1];
        }
        return name;
    }
    public string second(int num)
    {
        string name;
        if ((num == 0)||(num==1))
        {
         name = " ";
        }
        else
        {
            string[] arr1 = new string[] { "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety" };
            name = arr1[num - 2];
        }
        return name;
    }
    public string third(int num)
    {
        string name ;
        if (num == 0)
        {
            name = "";
        }
        else
        {
            string[] arr1 = new string[] { "Hundred" };
            name = arr1[0];
        }
        return name;
    }

}
}