private void ClearEdit(Control.ControlCollection AControls)
{
    foreach (Control vControl in AControls)
    {
        if (vControl is TextBox)
        {
            ((TextBox)vControl).Text = string.Empty;
        }
        else if (vControl is ComboBox)
        {
            ((ComboBox)vControl).Text = string.Empty;
        }
        else ClearEdit(vControl.Controls);
    }
}

private void button1_Click(object sender, EventArgs e)
{
    ClearEdit(Controls);
}