Numbers to Wave

using System;

namespace ConsoleApp88
{
    class Program
    {
        /// <summary>
        /// Program Entry
        /// </summary>
        /// <param name="args">Unused Args</param>
        static void Main(string[] args)
        {
            string input = string.Empty;

            do
            {
                try
                {
                    Console.WriteLine("Please enter a number: ");
                    input = Console.ReadLine();

                    // Fetch result if string is not empty
                    if (input != string.Empty)
                    {
                        string retVal = string.Empty;

                        // Add cents if not provided
                        if (!input.Contains(".")) input += ".0";

                        // Split string by . to dollars and cent
                        string[] i = input.Split('.');

                        // Get dollar value
                        retVal = NumbersToWav(int.Parse(i[0])) + " + dollars.wav";

                        // Get cent value
                        if (int.Parse(i[1]) > 0) retVal += " and " + NumbersToWav(int.Parse(i[1])) + " + cents.wav";

                        // Print result
                        Console.WriteLine(retVal + "\r\n");
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine("Error {0}\r\nPlease enter a valid number.\r\n", ex.Message);
                }

            } while (input != string.Empty);

        }

        /// <summary>
        /// Converts numeric value to .wav file names
        /// </summary>
        /// <param name="number">Number between -2,147,483,648 to +2,147,483,648</param>
        /// <returns>Concated .wav file names based on numbers</returns>
        public static string NumbersToWav(int number)
        {
            string retVal = string.Empty;

            if (number == 0) return "zero.wav";

            if (number < 0) return "minus.wav" + NumbersToWav(-number);

            if (number > 99) ResolveOver99(ref number, ref retVal);

            if (number > 0) ResolveLessThan100(number, ref retVal);

            return retVal; //.Trim().Trim('+').Trim();
        }

        /// <summary>
        /// Adds + sign if input is not empty
        /// </summary>
        /// <param name="input">String to append to</param>
        /// <returns>"+" + input</returns>
        public static string AddPlusSign(string input)
        {
            return (input == string.Empty ? string.Empty : " + ");
        }

        /// <summary>
        /// Resolves numbers over 99
        /// </summary>
        /// <param name="number">used to evaluate the number and returs remainder</param>
        /// <param name="retVal">used for results, appends to existing data</param>
        public static void ResolveOver99(ref int number, ref string retVal)
        {
            // Greater or equal to million
            if ((number / 1000000) > 0)
            {
                retVal += AddPlusSign(retVal) + NumbersToWav(number / 1000000) + " + million.wav"; // get millions value
                number %= 1000000; // set remainder from millions value
            }

            // Greater or equal to thousand
            if ((number / 1000) > 0)
            {
                retVal += AddPlusSign(retVal) + NumbersToWav(number / 1000) + " + thousand.wav"; // get thousands value
                number %= 1000; // set remainder from thousands value
            }

            // Greater or equal to hundred
            if ((number / 100) > 0)
            {
                retVal += AddPlusSign(retVal) + NumbersToWav(number / 100) + " + hundred.wav"; // get hundreds value
                number %= 100; // set remainder from hundreds value
            }
        }

        /// <summary>
        /// Resolves numbers less than 100
        /// </summary>
        /// <param name="number">used to evaluate the number</param>
        /// <param name="retVal">used for results, appends to existing data</param>
        public static void ResolveLessThan100(int number, ref string retVal)
        {
            if (number < 20)
            {
                retVal += AddPlusSign(retVal) + number + ".wav";
            }
            else
            {
                retVal += AddPlusSign(retVal) + (number - (number % 10)) + ".wav";
                if ((number % 10) > 0)
                {
                    retVal += AddPlusSign(retVal) + number % 10 + ".wav";
                }
            }
        }
    }
}