Get Excel Column Name in csharp

 public static string GetExcelColumn(string col_name, int IncrementValue)
        {
            string excelCol = string.Empty;
            int result = 0;

            // Process each letter.
            for (int i = 0; i < col_name.Length; i++)
            {
                result *= 26;
                char letter = col_name[i];

                // See if it's out of bounds.
                if (letter < 'A') letter = 'A';
                if (letter > 'Z') letter = 'Z';

                // Add in the value of this letter.
                result += (int)letter - (int)'A' + 1;
            }
            excelCol = GetExcelColumnName(result + IncrementValue);
            return excelCol;
        }
        private static string GetExcelColumnName(int col_num)
        {
            // See if it's out of bounds.
            if (col_num < 1) return "A";
            // Calculate the letters.
            string result = "";
            while (col_num > 0)
            {
                // Get the least significant digit.
                col_num -= 1;
                int digit = col_num % 26;

                // Convert the digit into a letter.
                result = (char)((int)'A' + digit) + result;

                col_num = (int)(col_num / 26);
            }

            return result;
        }