数字转拼音的实现方法

如何输入一个数值不超过2,000,000,000的数字串，把它输出为由小写英文字母和空格组成的字符串。就像是10010能输出为“yi wan ling yi shi”请各位大佬请教！

//数字转文字类
public class Cash
{
private static string MoneyNum = "零一二三四五六七八九";
private static string MoneyUnit = "十百千万十百千亿";
private static string CashUnit = "元角分整";
private static string[] BeforeReplace = new string[] { MoneyNum[0].ToString() + MoneyNum[0].ToString(),
MoneyUnit[7].ToString() + MoneyNum[0].ToString() + MoneyUnit[3].ToString() ,
MoneyNum[0].ToString() + MoneyUnit[3].ToString(),
MoneyNum[0].ToString() + MoneyUnit[7].ToString(),
MoneyUnit[7].ToString() + MoneyUnit[3].ToString(),
MoneyNum[0].ToString() + MoneyNum[0].ToString(),
MoneyNum[0].ToString() + /CashUnit[1].ToString() +/ MoneyNum[0].ToString() /+ CashUnit[2].ToString()/,
MoneyNum[0].ToString() /+ CashUnit[2].ToString()/
};
private static string[] AfterReplace = new string[] { MoneyNum[0].ToString(),
MoneyUnit[7].ToString() + MoneyNum[0].ToString(),
MoneyUnit[3].ToString() + MoneyNum[0].ToString(),
MoneyUnit[7].ToString() + MoneyNum[0].ToString(),
MoneyUnit[7].ToString() + MoneyNum[0].ToString(),
MoneyNum[0].ToString(),
String.Empty,
String.Empty
};

    /**//// <summary>
        /// 字符串替换方法，另外一种是以 4 个数字为基础的递归方法
        /// Create By HJ 2007-10-21
        /// </summary>
        /// <param name="moneyNum"></param>
        /// <returns></returns>
    public static string getCash(decimal moneyNum)
    {
        string intNum, point;
        /**////取整数部分
        intNum = Convert.ToString(Math.Floor(moneyNum));
        /**////取小数部分
        point = Convert.ToString(Math.Floor(moneyNum * 100));
        point = point.Substring(point.Length - 2);

        /**////计算整数部分
        for (int i = 0; i < MoneyNum.Length; i++)
        {
            intNum = intNum.Replace(i.ToString(), MoneyNum[i].ToString());
        }
        int intNumLength = intNum.Length;
        for (int i = intNumLength - 1; i > 0; i--)
        {   /**////根据位数把单位加上
                ///如果是零则不加单位，但是 万  和  亿 需要加上
            if (intNum[i - 1] == MoneyNum[0] && (intNumLength - i + 7) % 8 != 3 && (intNumLength - i + 7) % 8 != 7) continue;
            intNum = intNum.Insert(i, MoneyUnit[(intNumLength - i + 7) % 8].ToString());
        }

        /**////加上 角 和 分 的单位
        intNum += /*CashUnit[0].ToString() +*/ MoneyNum.Substring(Convert.ToInt16(point[0].ToString()), 1) /*+ CashUnit[1].ToString()*/ + MoneyNum.Substring(Convert.ToInt16(point[1].ToString()), 1) /*+ CashUnit[2].ToString()*/;

        /**////替换  零零 -> 零  亿零万  ->  亿零，零万  ->  万零，零亿 -> 亿零，亿万 -> 亿零，零角零分 - > ""，零分 - > ""，零零 -> 零，再调用一次，确保 亿零万 替换后的情况
        for (int i = 0; i < BeforeReplace.Length; i++)
        {
            while (intNum.IndexOf(BeforeReplace[i]) > -1)
            {
                intNum = intNum.Replace(BeforeReplace[i], AfterReplace[i]);
            }
        }

        /**////最后的 零 去掉
        if (intNum.EndsWith(MoneyNum[0].ToString())) intNum = intNum.Substring(0, intNum.Length - 1);

        return intNum /*+ CashUnit[3].ToString()*/;

    }
}

//然后文字转拼音，NuGet安装包Microsoft.International.Converters.PinYinConverter;
//使用方式：
public string GetPinYin(string num)
{
string nunlstr = string.Empty;
if (num.Length > 0)
{
for (int i = 0; i < num.Length; i++)
{
ChineseChar chineseChar = new ChineseChar(num[i]);
nunlstr += chineseChar.Pinyins[0] + " ";
}

        }
        return nunlstr;
    }