使用超过“字符计数”的字符计数；Z”；在C#中

我有一个数据集转储，它使用字符集类型的循环来查找第一个列字母。这对a-Z非常有效，但当我需要AA或AB时，我会不知所措。这是我正在使用的，是从我在网上找到的一些代码中重新编写的。我能做什么吗？

public void ExportToExcel(DataSet dataSet, string templatePath, int i, int h)
    {
        Excel.Application excelApp = new Excel.Application();
        excelApp.Visible = true;
        FileInfo excelFileInfo = new FileInfo(templatePath);
        Boolean fileOpenTest = IsFileLocked(excelFileInfo);

        Excel.Workbook templateBook;
        if (!fileOpenTest)
        { templateBook = excelApp.Workbooks.Open(templatePath); }
        else
        { templateBook = (Excel.Workbook)System.Runtime.InteropServices.Marshal.BindToMoniker(templatePath); }
        string tabName = lstQueryDumpSheet.Items[i].ToString();
        Excel.Worksheet templateSheet = templateBook.Sheets[tabName];
        // Copy DataTable
        foreach (System.Data.DataTable dt in dataSet.Tables)
        {
            // Copy the DataTable to an object array
            object[,] rawData = new object[dt.Rows.Count + 1, dt.Columns.Count];
            // Copy the values to the object array
            for (int col = 0; col < dt.Columns.Count; col++)
            {
                for (int row = 0; row < dt.Rows.Count; row++)
                { rawData[row, col] = dt.Rows[row].ItemArray[col]; }
            }
            // Calculate the final column letter
            string finalColLetter = string.Empty;
            string colCharset = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
            int colCharsetLen = colCharset.Length;
            if (dt.Columns.Count > colCharsetLen)
            { finalColLetter = colCharset.Substring((dt.Columns.Count - 1) / colCharsetLen - 1, 1); }
            finalColLetter += colCharset.Substring((dt.Columns.Count - 1) % colCharsetLen, 1);
            // Fast data export to Excel
            string dumpCellString = lstQueryDumpText.Items[i].ToString();
            string dumpCell = dumpCellString.Split('=').Last();
            string excelRange = string.Format(dumpCell + ":{0}{1}", finalColLetter, dt.Rows.Count + 1);
            templateSheet.get_Range(excelRange, Type.Missing).Value2 = rawData;
        }