数字转化为英文字符串 递归算法即可

        /// <summary>
        /// 数字转化为英文字符串 递归算法即可
        /// </summary>
        /// <param name="number"></param>
        /// <returns></returns>
        static string NumberToEnglishString(int number) 
        {
            if (number < 0) //暂不考虑负数
            {
                return "";
            }
            if (number < 20) //0到19
            {
                switch (number)
                {
                    case 0:
                        return "zero";
                    case 1:
                        return "one";
                    case 2:
                        return "two";
                    case 3:
                        return "three";
                    case 4:
                        return "four";
                    case 5:
                        return "five";
                    case 6:
                        return "sex";
                    case 7:
                        return "seven";
                    case 8:
                        return "eight";
                    case 9:
                        return "nine";
                    case 10:
                        return "ten";
                    case 11:
                        return "eleven";
                    case 12:
                        return "twelve";
                    case 13:
                        return "thirteen";
                    case 14:
                        return "fourteen";
                    case 15:
                        return "fifteen";
                    case 16:
                        return "sixteen";
                    case 17:
                        return "seventeen";
                    case 18:
                        return "eighteen";
                    case 19:
                        return "nineteen";
                    default:
                        return "";
                }
            }
            if (number < 100) //20到99
            {
                if (number % 10 == 0) //20,30,40,...90的输出
                {
                    switch (number)
                    {
                        case 20:
                            return "twenty";
                        case 30:
                            return "thirty";
                        case 40:
                            return "forty";
                        case 50:
                            return "fifty";
                        case 60:
                            return "sixty";
                        case 70:
                            return "seventy";
                        case 80:
                            return "eighty";
                        case 90:
                            return "ninety";
                        default:
                            return "";
                    }
                }
                else //21.22,....99 思路：26=20+6
                {
                    return string.Format("{0} {1}", NumberToEnglishString(10 * (number / 10)), 
                        NumberToEnglishString(number % 10));
                }
            }
            if (number < 1000) //100到999  百级
            {
                if (number % 100 == 0)
                {
                    return string.Format("{0} hundred", NumberToEnglishString(number / 100));
                }
                else 
                {
                    return string.Format("{0} hundred and {1}", NumberToEnglishString(number / 100), 
                        NumberToEnglishString(number % 100));
                }
            }
            if (number < 1000000) //1000到999999 千级
            {
                if (number % 1000 == 0)
                {
                    return string.Format("{0} thousand", NumberToEnglishString(number / 1000));
                }
                else
                {
                    return string.Format("{0} thousand and {1}", NumberToEnglishString(number / 1000), 
                        NumberToEnglishString(number % 1000));
                }
            }
            if (number < 1000000000) //1000 000到999 999 999 百万级
            {
                if (number % 1000 == 0)
                {
                    return string.Format("{0} million", NumberToEnglishString(number / 1000000));
                }
                else
                {
                    return string.Format("{0} million and {1}", NumberToEnglishString(number / 1000000), 
                        NumberToEnglishString(number % 1000000));
                }
            }
            if (number <= int.MaxValue) //十亿 级
            {
                if (number % 1000000000 == 0)
                {
                    return string.Format("{0} billion", NumberToEnglishString(number / 1000000000));
                }
                else
                {
                    return string.Format("{0} billion and {1}", NumberToEnglishString(number / 1000000000),
                        NumberToEnglishString(number % 1000000000));
                }
            }
            return "";
        }