Jei labai reikia pereit visus controlus stai rekursyvi OOP metodika:

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;


// Deklaruojam interfeisa kuris dirba su control
 public interface IControlAccessor
 {
      void Do (Control c);
 }

// Nusiveldime interfeisa ir sukuriame pvz Visible busenos verimo i atbula funkcionaluma
 public class VisibleInverter : IControlAccessor
 {
  #region IControlAccessor Members

  public void Do (Control c)
  {
   c.Visible = !c.Visible;
  }

  #endregion
 }

// Sukuriame rekursivine funkcija einancia per absoliuciai visus formos controlus ir sub sub controlus
// Tiesiog jei forma tures panele tai paneleje esantys controlai bus paneles.Controls propertyje
// Controls property priklauso Control tipui
 public class FormUtils
 {
  public static void AccessControls (
   Control control, 
   IControlAccessor accessor)
  {
   foreach (Control c in control.Controls)
   {
    accessor.Do (c);

    AccessControls (c, accessor);
   }
  }
 }

// Iskvieciame visu formos controlu apdirbima
 public partial class Form1 : Form
 {
  public Form1 ()
  {
   InitializeComponent ();

   FormUtils.AccessControls (this, new VisibleInverter ());
  }
 }



Tuo paciu jei reikia apdirbti kazkoki konkretu controla kazkaip ipatingai, galima tai daryti su "is" pvz


 public class OtherAccessor : IControlAccessor
 {
  #region IControlAccessor Members

  public void Do (Control c)
  {
   if(c is TextBox) {
        // Assigninimas castinant
        TextBox t = (TextBox)c;
        TextBox.Clear();
    }
    else if (c is ComboBox){
        // Accessinimas be assigninimo
        ((ComboBox)c).SelectedIndex = 0;
    }    

    // ir t.t...
  }

  #endregion
 }


P.S. Parasyta viskas per 5 min ;)