between two dates for Msaccess database...

Assuming that there are selected dates in both DateTimePicker controls, I don't understand the error message about there being no value assigned to one or more parameters.

Can you re-post the code as you currently have it, please.



 

@Vulpes
when I do this:
if (param1.Value <= param2.Value) 
Its says that Operator '<=' cannot be applied to operands of type 'object' and 'object'
then I change to this:
if (datainicialReservasviaturas.Value.Date <= datafinalReservasviaturas.Value.Date) 
Then its says:
Não foi fornecido nenhum valor para um ou mais parâmetros necessários.
no value have been gave for one or more parameter necessary 

Try:

private void dataReservasviaturas_ValueChanged(object sender, EventArgs e)
{
   conn.Open();
   OleDbCommand cmd = conn.CreateCommand();
   cmd.CommandType = CommandType.Text;
   cmd.CommandText = "select * from personel where dataworkers between ? and ?";
   var param1 = new OleDbParameter("@StartDate", OleDbType.Date);
   var param2 = new OleDbParameter("@EndDate", OleDbType.Date);
   param1.Value = dateTimePicker1.Value.Date;
   param2.Value = dateTimePicker2.Value.Date;

   if (dt1 <= dt2)
   {
     cmd.Parameters.Add(param1);
     cmd.Parameters.Add(param2);
   }
   else
   {
     cmd.Parameters.Add(param2);
     cmd.Parameters.Add(param1);
   }

   cmd.ExecuteNonQuery();
   DataTable dt = new DataTable();
   OleDbDataAdapter da = new OleDbDataAdapter(cmd);
   da.Fill(dt);
   conn.Close();
   dataGridView1.DataSource = dt;
}