///use this to cycle through the controls collection and clear all textboxes

  private void btnClear_Click(object sender, EventArgs e)
        {
                //---this sub finds all the textboxes on the form and clears them! It searches through the controls collection and when
                //    it finds a textbox, it clears it.
                //---dim a temp object variable as a control object. It can be a button, listbox, textbox, etc.
                       
                foreach (Control myControl in Controls)    //loop through the form's control collection to find all the textboxes.
                    {
                        if (myControl is TextBox)              //found textbox? then clear text
                            myControl.Text = "";
                               
                    }
        
                    txtNumber1.Focus();
         
        }