Excel标题与索引的对应关系

/// <summary>
        /// 返回对应标题的索引
        /// </summary>
        /// <param name="columnTitle">Excel定义列标题:大写字母</param>
        /// <returns>索引从0开始</returns>
        public static int GetColumnIndex(string columnTitle)
        {
            int len = columnTitle.Length - ;
            int index = ;
            for (int i = len; i >=; i--)
            {
                index += GetColumnTitleNumber(columnTitle[i])*Convert.ToInt32(Math.Pow(, len - i));
            }
            return --index;
        }

        private static int GetColumnTitleNumber(char columnTitle)
        {
            int startNumber = Convert.ToInt32('A');
            int currentNumber = Convert.ToInt32(columnTitle);
            if (currentNumber < startNumber || currentNumber >= startNumber + )
                throw new ArgumentOutOfRangeException(columnTitle+"列标题超出定义");
            return Convert.ToInt32(columnTitle) - startNumber + ;
        }

        /// <summary>
        /// 根据列的索引返回对应的标题
        /// </summary>
        /// <param name="columnIndex">列索引从0开始</param>
        /// <returns></returns>
        public static string GetColumnTitle(int columnIndex)
        {
            int columnNumber = columnIndex + ;
            int left = columnNumber/;
            int startNumber = Convert.ToInt32('A');
            if (left ==  || (left ==  && (columnNumber% == )))
            {
                return ((char) (startNumber + columnNumber - )).ToString();
            }
            if (columnNumber% == )
                left--;
            return GetColumnTitle(left) + GetColumnTitle(columnNumber - left * );
        }