Append new columns to excel sheet, using C#

I would look at it like just doing VBA in Excel. Check to see which columns have values, and then just use the the next row.

The way to change values:

sheet.Cells[row, column] = value;

Similarly you can get values from cells.

Here is the solution for my question.

public static void AddNewColumn(string fileName, int sheetNum)
    {
        Excel.Application xlApp;
        Excel.Workbook xlWorkBook;
        Excel.Worksheet xlWorkSheet;
        Excel.Range rng;
        object misValue = System.Reflection.Missing.Value;

        try
        {
            xlApp = new Excel.Application();
            xlApp.Visible = true;
            xlWorkBook = xlApp.Workbooks.Open(fileName, 0, false, 5, "", "", false,
                Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "", true, false, 0, true, 1, 0);   //@"H:\TestFile.xlsx"
            xlWorkSheet = (Excel.Worksheet)xlWorkBook.Sheets.get_Item(sheetNum);
            //xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(sheetNum);
            rng = xlWorkSheet.UsedRange;

            int colCount = rng.Columns.Count;
            int rowCount = rng.Rows.Count;
            rng = (Excel.Range)xlWorkSheet.Cells[rowCount, colCount];
            Excel.Range newColumn = rng.EntireColumn;
            xlWorkSheet.Cells[1, colCount + 1] = "Visit Link";

            //save and quit
            //xlWorkBook.SaveAs(@"H:\TestFile.xlsx", misValue, misValue, misValue, misValue, misValue,
            //    Excel.XlSaveAsAccessMode.xlExclusive, misValue, misValue, misValue, misValue, misValue);
            xlWorkBook.Save();
            xlWorkBook.Close(misValue, misValue, misValue);
            xlApp.Quit();

            // release all the application object from the memory
            System.Runtime.InteropServices.Marshal.ReleaseComObject(rng);
            System.Runtime.InteropServices.Marshal.ReleaseComObject(xlWorkSheet);
            Marshal.ReleaseComObject(xlWorkBook);
            Marshal.ReleaseComObject(xlApp);
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }
        finally
        {

            GC.Collect();
            GC.WaitForPendingFinalizers();
        }
    }

private void btnAddNewColumns_Click(object sender, EventArgs e)
       {
           try
           {
               string theFile = txtFileName.Text;
               int theSheet = cboGetSheet.SelectedIndex +1;
               ExcelTools.AddNewColumn(theFile, theSheet);
           }
           catch (Exception ex)
           {
               MessageBox.Show(ex.ToString());
           }
       }

Hi, have a check at this; Summarize C# Control Excel Skills[^].
This is a good collection of skills.

Good Luck.