c# excel的列转换成数字

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.Regularexpression_rs;
 
namespace Hooogle
{
    public static class ExcelConvert
    {
        #region - 由数字转换为Excel中的列字母 -
        
        public static int ToIndex(string columnName)
        {
            if (!Regex.IsMatch(columnName.ToUpper(), @"[A-Z]+")) { throw new Exception("invalid parameter"); }
 
            int index = 0;
            char[] chars = columnName.ToUpper().ToCharArray();
            for (int i = 0; i < chars.Length; i++)
            {
                index += ((int)chars[i] - (int)‘A‘ + 1) * (int)Math.Pow(26, chars.Length - i - 1);
            }
            return index - 1;
        }
 
        
        public static string ToName(int index)
        {
            if (index < 0) { throw new Exception("invalid parameter"); }
 
            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());
        }
        #endregion
    }
}