foreach on multiple textboxes

Hello guys,
I need some help regarding a foreach on multiple textboxes.
The code is this
protected void Button1_Click(object sender, EventArgs e)
        {

            foreach (Control c in Panel1.Controls)
            {
                if (c is TextBox)
                {
                    TextBox t = (c as TextBox);
                    if (t.Text.Length == 0)
             &nbs ...