Convert Currency to English Words

#region Namespace
using System;
using System.Text;
using System.Text.RegularExpressions;
#endregion

#region Copyright©

#endregion

public class CurrencyTranslator
{
    // Array of sting to hold the words from one to nineteen 
    private string[] _arrayOfOnes = { string.Empty, "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", 
        "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", 
        "Nineteen" };
    // Array of string to hold the words of tens - 10, 20,.., 90
    private string[] _arrayOfTens = { string.Empty , "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", 
        "Seventy", "Eighty", "Ninety"};
    
    // Converts the decimal to currency
    public string TranslateCurrency(decimal currencyValue)
    {
        string numericCurrency = currencyValue.ToString().Trim ();
        //Check for the max capacity limit of the input 
        if (numericCurrency.Length > 18)
          return "Invalid input format";

        string leftValue, decimalWord;
        //Right align the charecters with padding of "0" to length the of 18 charecters
        if (numericCurrency.IndexOf(".") >= 0)
        {
            leftValue = numericCurrency.Substring(0, numericCurrency.IndexOf(".")).PadLeft(18, Convert.ToChar("0"));
            decimalWord = numericCurrency.Substring(numericCurrency.IndexOf(".") + 1).PadRight(2, Convert.ToChar("0"));
            decimalWord = (decimalWord.Length > 2 ? decimalWord.Substring(0, 2) : decimalWord);
        }
        else
        {
            leftValue = numericCurrency.PadLeft(18, Convert.ToChar("0"));
            decimalWord = "0";
        }

        string quadrillionWord, trillionWord, billionWord, millionWord, thousandWord, hundredWord;
        quadrillionWord = TranslateHundreds(Convert.ToInt32(leftValue.Substring(0, 3))); // One Quadrillion - Number of zeros 15
        trillionWord = TranslateHundreds(Convert.ToInt32(leftValue.Substring(3, 3)));    // One Trillion - Number of zeros 12
        billionWord = TranslateHundreds(Convert.ToInt32(leftValue.Substring(6, 3)));     // One Billion - Number of zeros 9
        millionWord = TranslateHundreds(Convert.ToInt32(leftValue.Substring(9, 3)));    // One Million - Number of zeros 6
        thousandWord = TranslateHundreds(Convert.ToInt32(leftValue.Substring(12, 3)));
        hundredWord = TranslateHundreds(Convert.ToInt32(leftValue.Substring(15, 3)));
        decimalWord = TranslateDecimal(decimalWord);

         // Start building the currency
        StringBuilder currencyInEnglish = new StringBuilder();
        currencyInEnglish.Append((quadrillionWord.Trim() == string.Empty ? string.Empty : quadrillionWord + " Quadrillion "));
        currencyInEnglish.Append((trillionWord.Trim() == string.Empty ? string.Empty : trillionWord + " Trillion "));
        currencyInEnglish.Append((billionWord.Trim() == string.Empty ? string.Empty : billionWord + " Billion "));
        currencyInEnglish.Append((millionWord.Trim() == string.Empty ? string.Empty : millionWord + " Million "));
        currencyInEnglish.Append((thousandWord.Trim() == string.Empty ? string.Empty : thousandWord + " Thousand "));
        currencyInEnglish.Append((hundredWord.Trim() == string.Empty ? string.Empty : hundredWord));

        currencyInEnglish.Append(currencyInEnglish.ToString() == string.Empty ? "Zero Dollars " : " Dollars");
        if (currencyInEnglish.ToString().StartsWith("One Dollars"))
        {
            currencyInEnglish.Replace("One Dollars", "One Dollar");
        }
        currencyInEnglish.Append((decimalWord == string.Empty ? " and Zero Cents" : " and " + decimalWord + " Cents"));
        return currencyInEnglish.ToString();
    }
  

    #region Private Functions
   

    private string TranslateHundreds(int value)
    {
        string result;
       // If the value is less than hundred then convert it as tens 
        if (value <= 99)
        {
            result = (TranslateTens(value));
        }
        else
        {
            result = _arrayOfOnes[Convert.ToInt32(Math.Floor(Convert.ToDecimal(value / 100)))];
            // Math.Floor method is used to get the largest integer from the decial value
            result += " Hundred ";
            // The rest of the decimal is converted into tens
            if (value - Math.Floor(Convert.ToDecimal((value / 100) * 100)) == 0)
            {
                result += string.Empty;
            }
            else
            {
                result += string.Empty + TranslateTens(Convert.ToInt32(value - Math.Floor(Convert.ToDecimal((value / 100) * 100))));
            }
        }
        return result;
    }
    

    private string TranslateTens(int value)
    {
        string result;
        // If the value is less than 20 then get the word directly from the array
        if (value < 20)
        {
            result = _arrayOfOnes[value];
            value = 0;
        }
        else
        {
            result = _arrayOfTens[(int)Math.Floor(Convert.ToDecimal(value / 10))];
            value -= Convert.ToInt32(Math.Floor(Convert.ToDecimal((value / 10) * 10)));
        }
        result = result + (_arrayOfOnes[value].Trim() == string.Empty ? string.Empty : "-" + _arrayOfOnes[value]);
        return result;
    }

    // Translates the decimal part of the currency to words
    private string TranslateDecimal(string value)
    {
        string result = string.Empty;
        // Check whether the decimal part starts with a zero. Example : 12.05
        if (value != "0")
        {
            if (value.StartsWith("0"))
            {
                result = "Zero ";
                result += _arrayOfOnes[Convert.ToInt32(value.Substring(1, 1))];
            }
            else
            {
                result = TranslateTens(Convert.ToInt32(value));
            }

        }
        return result;
    }
    #endregion
}