C#数字转英文（1 -＞ one ）

/// <summary>
/// 数字转为英文字符串 不考虑负数
/// </summary>
/// <param name="number"></param>
/// <returns></returns>
public static string NumberToEnglishString(int number)
 {
     if (number < 0) 
     {
         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 "";
 }