C#: Looping through the Controls Collections
dot net controls are child controls of the form so you have to identify the name of the form first.

     //form2 is the name of the html form. Look at source view.
        foreach (Control ctrl in Page.FindControl("Form2").Controls)  
        {
            if (ctrl is TextBox)
                
              ((TextBox)ctrl).Text = "";
              
        }