1、2、3、4 转换成 A、B、C、D

        static void Main(string[] args)
        {
            Console.WriteLine("1  :" + ColNumnerToColCode(1));
            Console.WriteLine("2  :" + ColNumnerToColCode(2));
            Console.WriteLine("3  :" + ColNumnerToColCode(3));
            Console.WriteLine("4  :" + ColNumnerToColCode(4));
            Console.WriteLine("27 :" + ColNumnerToColCode(27));
            Console.WriteLine("36 :" + ColNumnerToColCode(36));
            Console.WriteLine("703:" + ColNumnerToColCode(703));
            Console.Read();
        }

        /// <summary>
        /// 将列号转换为Excel中的列字母
        /// </summary>
        /// <param name="index"></param>
        /// <returns></returns>
        static string ColNumnerToColCode(int index)
        {
            if (index <= 0)
                throw new Exception("invaild parameter");
            index--;
            List<string> chars = new List<string>();
            do
            {
                if (chars.Count > 0)
                    index--;
                chars.Insert(0, ((char)(index % 26 + (int)'A')).ToString());
                index = (int)((index - index % 26) / 26);
            } while (index > 0);

            return String.Join(string.Empty, chars.ToArray());
        }

输出：