using System;
using System.Collections.Generic;
using System.Text;

namespace Spell
{
    public class SpellNumbers
    {
        private static string[] r_positionArray = { "", " thousand", " million", " billion", " trillion", " quadrillion", " quintillion" };
        private static string[] r_digitArray = { "", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };
        private static string[] r_tensArray = { "", "", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety" };
        private static string[] r_teensArray = { "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" };

        public static string SpellNum(long num)
        {
            bool negative = false;
            if (num == 0)
            {
                return "zero";
            }
            if (num < 0)
            {
                num = -num;
                negative = true;
            }

            StringBuilder sb = new StringBuilder();
            int pos = 0;
            while (num > 0)
            {
                if (num % 1000 != 0)
                {
                    sb.Insert(0, SpellThreeDigits((int)(num % 1000)) + r_positionArray[pos]);
                }
                if (num / 1000 != 0)
                {
                    sb.Insert(0, ", ");
                }
                num /= 1000;
                pos++;
            }
            if (negative)
            {
                sb.Insert(0, "negative ");
            }

            return sb.ToString();
        }

        private static string SpellThreeDigits(int threeDigits)
        {
            StringBuilder sb = new StringBuilder();
            if (threeDigits / 100 != 0)
            {
                sb.Append(r_digitArray[threeDigits / 100] + " hundred");
                if (threeDigits % 100 != 0)
                {
                    sb.Append(" ");
                }
            }

            int tensDigit = threeDigits % 100 / 10;
            int onesDigit = threeDigits % 10;
            if (tensDigit == 1)
            {
                sb.Append(r_teensArray[onesDigit]);
            }
            else
            {
                sb.Append(r_tensArray[tensDigit]);
                if (tensDigit != 0 && onesDigit != 0)
                {
                    sb.Append(" ");
                }
                sb.Append(r_digitArray[onesDigit]);
            }
            return sb.ToString();
        }

    }
}