how to open existing worksheet

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C#

C#4.0

hi,

am developing attendance system, when i swipe the card , i will get card Id into text box, then i need to insert into excel in button click.

here is the code:

private void button1_Click(object sender, EventArgs e)
       {
           if(txtCardID.Text !="")
           {
               newString = "";
               string connectionString = GetConnectionString();
               string s = Convert.ToString(Program.ConnectObj.Output);
               if (s.Length == 7)
               {

                   newString = s.PadLeft(10, '0');
               }
               else if (s.Length == 8)
               {

                   newString = s.PadLeft(10, '0');
               }
               else if (s.Length == 9)
               {

                   newString = s.PadLeft(10, '0');
               }

               using (OleDbConnection conn = new OleDbConnection(connectionString))
               {
                   conn.Open();
                   OleDbCommand cmd = new OleDbCommand();
                   cmd.Connection = conn;

                   cmd.CommandText = "CREATE TABLE [sheet1] (id INT);";
                   cmd.ExecuteNonQuery();

                   cmd.CommandText = "INSERT INTO [sheet1$](id) VALUES('" + newString + "');";
                   cmd.ExecuteNonQuery();
                   MessageBox.Show("Successfully Inserted");

                   conn.Close();
               }
               txtCardID.Text = "";
           }
           else
               MessageBox.Show("Please Swipe the Card");


       }

first time it's creating "sheet1" writes card id into that, but for next time it's giving Exception as "sheet1 already exists" how to solve it.

am using oledb connection.

private string GetConnectionString()
       {
           Dictionary<string, string> props = new Dictionary<string, string>();

           // XLSX - Excel 2007, 2010, 2012, 2013
           props["Provider"] = "Microsoft.ACE.OLEDB.12.0;";
           props["Extended Properties"] = "Excel 12.0 XML";
           string appPath = Path.GetDirectoryName(Application.ExecutablePath);
           string fName = @appPath + "\\MyExcel.xlsx ";
            props["Data Source"] = fName;
          // props["Data Source"] = "C:\\MyExcel.xlsx";

           StringBuilder sb = new StringBuilder();

           foreach (KeyValuePair<string, string> prop in props)
           {
               sb.Append(prop.Key);
               sb.Append('=');
               sb.Append(prop.Value);
               sb.Append(';');
           }

           return sb.ToString();
       }