C#编写程序将数字转换成英文：如32：thirty two ,123：one hundred and twenty three.说明：1、输入文件格式为input.txt,输出文件格式为output.txt；2、数字为正整数,长度不超过十位,不考虑小数,转化结果为

C#编写程序将数字转换成英文：如32：thirty two ,123：one hundred and twenty three.说明：1、输入文件格式为input.txt,输出文件格式为output.txt；2、数字为正整数,长度不超过十位,不考虑小数,转化结果为
C#编写程序将数字转换成英文：如32：thirty two ,123：one hundred and twenty three.
说明：
1、输入文件格式为input.txt,输出文件格式为output.txt；
2、数字为正整数,长度不超过十位,不考虑小数,转化结果为英文小写 ；
3、输出格式为100=one hundred （参考out.txt ）；
4、非法数据请返回“error”,不存在空行；
5、关键词提示：billion ,million,thousand ,hundred .
ps:
input.txt的文本信息为：
0
01
10
11
99
100
101
199
999
1001
9999
10000
100000
100001
1000000
10000000
100000001
1020300401
102a300401
是个体
output文件
0=zero
01=one
10=ten
11=eleven
99=ninety nine
100=one hundred
101=one hundred and one
199=one hundred and ninety nine
999=nine hundred and ninety nine
1001=one thousand one
9999=nine thousand nine hundred and ninety nine
10000=ten thousand
100000=one hundred thousand
100001=one hundred thousand one
1000000=one million
10000000=ten million
100000001=one hundred million one
1020300401=one billion twenty million three hundred thousand four hundred and one
102a300401=error
是个体=error

C#编写程序将数字转换成英文：如32：thirty two ,123：one hundred and twenty three.说明：1、输入文件格式为input.txt,输出文件格式为output.txt；2、数字为正整数,长度不超过十位,不考虑小数,转化结果为
static void Main(string[] args)
        {
            string readFilePath = AppDomain.CurrentDomain.BaseDirectory + "input.txt";
            List<string> list = ReadFile(readFilePath);
            
            //写文件,将每一行写入文件中
            string writeFilePath = AppDomain.CurrentDomain.BaseDirectory + "output.txt";
            FileStream fs = new FileStream(writeFilePath, FileMode.Create, FileAccess.ReadWrite);
            StreamWriter sw = new StreamWriter(fs, System.Text.Encoding.GetEncoding("gb2312"));
            int number;
            for (int i = 0; i < list.Count; i++)
            {
                string output = "";
                if (int.TryParse(list[i], out number) == false)
                {
                    output = "error";
                }
                else 
                {
                    output = NumberToEnglishString(number);
                }
                sw.WriteLine("{0}={1}", list[i], output);
            }
            sw.Close();
            fs.Close();
            //程序结束后在debug文件夹下会生成output.txt
            Console.ReadLine();            
        }
        /// <summary>
        /// 读取文件 将每一行添加到集合中
        /// </summary>
        /// <param name="path"></param>
        /// <returns></returns>
        public static List<string> ReadFile(string path) 
        {
            List<string> list = new List<string>();
            FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read);
            StreamReader sr = new StreamReader(fs, System.Text.Encoding.GetEncoding("gb2312"));            
            string s = sr.ReadLine();
            while (s != null)
            {
                if (s.Length > 0)
                {
                    list.Add(s);
                }
                s = sr.ReadLine();
            }
            sr.Close();
            fs.Close();
            return list;
        }
        /// <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 "";
                    }
                }
  &n