用C#写一个CheckWriter的控制台程序，如果你在银行工作，需要一个系统能够当你输入一串数字金额后能用其对应的英文输出，这样方便打印在支票上防止篡改。用户输入一个0到20亿的数字包含最多2位小数，将其转换为英文输出。例如输入1258276.25，能够输出：one million, three hundred and fifty seven thousand, two hundred and fitty six DOLLARS AND thirty two CENTS.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CheckWriter
{
    class Program
    {
        private static string[] _lessTwentyNumbers = new string[]{"Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight",
              "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen","Sixteen", "Seventeen", "Eighteen", "Nineteen"};
        private static string[] _lessHundredNumbers = new string[]{"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty","Ninety"};
        private static string[] _scaleNumbers = new string[] { "", "Thousand", "Million", "Billion" };
        
        static void Main(string[] args)
        {
            string s = ConvertDecimalToWords(1258276.25);
            Console.WriteLine(s);
            Console.Read();
        }

        /// <summary>
        /// 将数字转为英文描述
        /// </summary>
        /// <param name="number"></param>
        /// <returns></returns>
        private static string ConvertNumberToWords(int number)
        {
            if (number == 0)
            {
                return _lessTwentyNumbers[0];
            }

            int[] digitGroups = new int[4];

            int positive = Math.Abs(number);

            // 将数字按三位一段保存到数组里
            for (int i = 0; i < 4; i++)
            {
                digitGroups[i] = positive % 1000;
                positive /= 1000;
            }

            string[] groupText = new string[4];

            for (int i = 0; i < 4; i++)
            {
                // 每三位一段转为相应的英文字符
                groupText[i] = ConvertThreeDigitToWords(digitGroups[i]);
            }

            string combined = groupText[0];

            for (int i = 1; i < 4; i++)
            {
                if (digitGroups[i] != 0)
                {
                    // 每一段加上相应的这一段的级别数字
                    string prefix = groupText[i] + " " + _scaleNumbers[i];

                    if (!string.IsNullOrEmpty(prefix))
                    {
                        if (string.IsNullOrEmpty(combined))
                        {
                            combined = prefix;
                        } 
                        else
                        {
                            combined = prefix + ", " + combined;
                        }
                    }
                }
            }

            if (number < 0)
            {
                combined = "Negative " + combined;
            }

            return combined;
        }

        /// <summary>
        /// 处理三位数以内的数字转为英文描述
        /// </summary>
        /// <param name="threeDigits"></param>
        /// <returns></returns>
        private static string  ConvertThreeDigitToWords(int threeDigits)
        {
            string groupText = "";
            // 获取百位
            int hundreds = threeDigits / 100;
            int tensUnits = threeDigits % 100;
            if (hundreds != 0)
            {
                groupText += _lessTwentyNumbers[hundreds] + " Hundred";

                if (tensUnits != 0)
                {
                    groupText += " and ";
                }
            }

            // 获取十位
            int tens = tensUnits / 10;
            int units = tensUnits % 10;
            if (tens >= 2)
            {
                groupText += _lessHundredNumbers[tens];
                if (units != 0)
                {
                    groupText += " " + _lessTwentyNumbers[units];
                }
            }
            else if (tensUnits != 0)
            {
                groupText += _lessTwentyNumbers[tensUnits];
            }

            return groupText;
        }

        private static string ConvertDecimalToWords(double number)
        {
            int i = (int)number;
            int p = (int)((number - i) * 100);
            return ConvertNumberToWords(i) + " DOLLARS AND " + ConvertNumberToWords(p) + " CENTS";
        }
    }
}

上面的代码中两个核心函数是ConvertNumberToWords和ConvertThreeDigitToWords，ConvertThreeDigitToWords的作用主要是能将小于1000的整数转为相应的金额，而ConvertNumberToWords负责将不同段的金额组合成完整的金额，主要是加上了该金额对应的位，例如本程序由于只要求对20亿以内的数字进行处理，因此分为千，百万和十亿三档。理解好了这两个函数基本就能知道是怎么做的。