FindControlIterative.cs

using System.Collections.Generic;

// accesses a control by ID (i.e. a checkbox/button/textbox etc)
private static Control FindControlIterative(Control root, string id)
{       
        Control ctl = root;
        LinkedList<Control> ctls = new LinkedList<Control>();
        while (ctl != null)
        {
                if (ctl.ID == id)
                return ctl;

                foreach (Control child in ctl.Controls)
                {
                    if (child.ID == id)
                        return child;

                    if (child.HasControls())
                        ctls.AddLast(child);
                }

                ctl = ctls.First.Value;
                ctls.Remove(ctl);
        }

        return null;
}

// To call the method, use something like:
public MainMethod()
{
        // get a textbox that has the ID "address"
        TextBox txt = FindControlIterative(control, "address") as TextBox;

        // change the text of that textbox
        txt.Text = "some text";
}