Update

Question

Hiiii....i have the following code for updating database but am gettin error like "Object reference not set to an instance of an object" please help me..

 private void btnUpdate_Click(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection();
            SqlCommand cmd = new SqlCommand();
            SqlDataAdapter da = new SqlDataAdapter();
            string strConnection = "Integrated Security=SSPI;Persist Security Info=False;User ID=CRYSYS1-DESKTOP\\SQLEXPRESS\\Student;Initial Catalog=ipRFID;Data Source=CRYSYS1-DESKTOP\\SQLEXPRESS";
            con = new SqlConnection(strConnection);
            con.Open();
            string command = "UPDATE TB_EmployeeMaster set Version=@Version,Operating System=@OS,Processor=@Processor,RAM=@RAM where RecId='" + txtID.Text + "'";

            cmd = new SqlCommand(command,da.SelectCommand.Connection);
            cmd.Parameters.AddWithValue("@RecId", txtID.Text);
            cmd.Parameters.AddWithValue("@Version", txtVersion.Text);
            cmd.Parameters.AddWithValue("@OS", txtOS.Text);
            cmd.Parameters.AddWithValue("@Processor", txtProcessor.Text);
            cmd.Parameters.AddWithValue("@RAM", txtRAM.Text);
            DataSet ds = new DataSet();
            da.UpdateCommand = cmd;

            da.Fill(ds, "TB_EmployeeMaster");
            da.Update(ds, "TB_EmployeeMaster");
            //cmd.ExecuteNonQuery();
            MessageBox.Show("Updated");

            con.Close();
}