根据列序号生成excel英文列名

       /// <summary>
       /// 获取列序号对应的excel的列英文字母名称(如27：AA)
       /// </summary>
       /// <param name="columnIndex"></param>
       /// <returns></returns>
       public static string getExcelColumnName(int columnIndex)
       {
           Console.WriteLine(columnIndex.ToString());
           columnIndex++;
           //获取26个大写英文字母
           int A = 65;
           char[] cArry = new char[27];

           for (int i = 1; i < 27; i++)
           {
               cArry[i] = (char)(A + i - 1);

           }
           int azValue = 26;

           //如果小于26直接返回对应的26进制字符
           if (columnIndex < azValue + 1)
           {
               return cArry[columnIndex].ToString();
           }

           int mode = 0;
           List<char> azArry = new List<char>();
           List<int> azCodeArry = new List<int>();