title: updating excel sheet in c# using iterop.excel
body: <p>I am trying updating a excel sheet in c# and i am using interop.excel.
  When i update a excel sheet this is update a single data.
  I want all data update in a single excel sheet.
  I am using this code</p>
  
  <pre><code>`private void button1_Click(object sender, EventArgs e)
      {
          if (cnt1 &gt;= 1)
          {
              connectionSilca();
              for (int counter = 0; counter &lt; cnt1; counter++)
              {
                  fcl.cmd = new OracleCommand("select book_id,book_title,category_id,author,book_pub,book_copies,publisher_name,isbn,copyright_year,date_added,status from book where book_id='" + listBox1.Items[counter].ToString() + "'", fcl.con);
  
                  DataTable dt = new DataTable();
                  DataSet DS = new DataSet();
                  OracleDataAdapter AD = new OracleDataAdapter(cmd);
                  OracleDataAdapter da = new OracleDataAdapter(cmd);
                  da.Fill(dt);
                  da.Fill(DS);
                  //DataTable temptable = DS.Tables[0];
                  //ExportToExcel(temptable);
                  ExportToExcel(DS.Tables[0]);
              }
          }
          else
          {
              MessageBox.Show("Please Select Atleast One Item");
          }
          con.Close();
          MessageBox.Show("EXCEL DOWNLOAD SUCCESSFULLY");
          datarefresh();
      }
  
      public void ExportToExcel(DataTable dtCollection)
      {
          var ds = dtCollection;
          Microsoft.Office.Interop.Excel.Worksheet objWorkSheet1 = null;
          Microsoft.Office.Interop.Excel.Application objExcel = new Microsoft.Office.Interop.Excel.Application { Visible = false };
          Microsoft.Office.Interop.Excel.Workbooks objWorkbooks = objExcel.Workbooks;
          Microsoft.Office.Interop.Excel.Workbook objWorkbook = objWorkbooks.Add(Missing.Value);
          Microsoft.Office.Interop.Excel.Sheets objSheets = objWorkbook.Worksheets;
          Microsoft.Office.Interop.Excel.Range objCells;
          Microsoft.Office.Interop.Excel.Range myCell;
  
          //open the excel file form the location 
          //here is existing excel code
          string path = @"C:\\EXCEL\\DATA\\myData.xls";
          objExcel = new Microsoft.Office.Interop.Excel.Application();
          objExcel.DisplayAlerts = false;
          objWorkbook = objExcel.Workbooks.Open(path, 0, false, 5, "", "", false, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "", true, false, 0, true, false, false);
          //Get all the sheets in the workbook
          objSheets = objWorkbook.Worksheets;
          //Get the allready exists sheet
          objWorkSheet1 = (Microsoft.Office.Interop.Excel.Worksheet)objSheets.get_Item("Input");
          Microsoft.Office.Interop.Excel.Range range = objWorkSheet1.UsedRange;
  
          objWorkSheet1.Cells[5, 3]= 100000089;
          objWorkSheet1.Cells[5, 4] = 001;
          objWorkSheet1.Cells[5, 7] = System.DateTime.Now.ToString("ddMMyyyy");
          objWorkSheet1.Cells[5, 10] = "ASHSBCTS2017";
  
          var iCurrentRow = 12;
          var dt = ds;
          int columnsCount = dt.Columns.Count;
          objWorkSheet1 = (Microsoft.Office.Interop.Excel.Worksheet)(objSheets[1]);
          objCells = objWorkSheet1.Cells;
  
          /*for (var h = 0; h &lt; dt.Columns.Count; h++)
          {
              myCell = (Microsoft.Office.Interop.Excel.Range)objCells[iCurrentRow, h + 1];
              myCell.Value2 = dt.Columns[h].ColumnName;
          }
          iCurrentRow++;*/
          for (var r = 0; r &lt; dt.Rows.Count; r++)
          {
              for (var c = 0; c &lt; dt.Columns.Count; c++)
              {
                      if (dt.Columns[c].DataType.Name == "String" || dt.Columns[c].DataType.Name == "DateTime")
                      {
                          myCell = (Microsoft.Office.Interop.Excel.Range)objCells[r + iCurrentRow, c + 1];
                          myCell.Value2 = "'" + dt.Rows[r][c].ToString().Trim();
                      }
                      else
                      {
                          myCell = (Microsoft.Office.Interop.Excel.Range)objCells[r + iCurrentRow, c + 1];
                          myCell.Value2 = dt.Rows[r][c];
                      }
                  }
              }
          //objWorkSheet1.Cells.EntireRow.AutoFit();
          //objWorkSheet1.Cells.EntireColumn.AutoFit();
          objWorkbook.SaveAs("C:\\EXCEL\\DATA\\myData.xls", Microsoft.Office.Interop.Excel.XlFileFormat.xlExcel12, System.Reflection.Missing.Value, 
              System.Reflection.Missing.Value, false, false, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlShared, false, false,
              System.Reflection.Missing.Value, System.Reflection.Missing.Value, System.Reflection.Missing.Value);
          objWorkbook.Close(Missing.Value, Missing.Value, Missing.Value);
          objExcel.Quit();
          GC.WaitForPendingFinalizers();
          GC.Collect();
          GC.WaitForPendingFinalizers();
          GC.Collect();
      }`
  </code></pre>
  
  <p>How to solve this, please give me some solution for this 
  Thanks in advance</p>