How to find controls from aspx page on c# in loop

Find element on a page runtime

aspx page

<asp:updatepanel id="updatepanel1" runat="server">
<contenttemplate>
<asp:TextBox id="txtName_1" runat="server"/>
<asp:TextBox id="txtName_2" runat="server"/>
<asp:TextBox id="txtName_3" runat="server"/>
<contenttemplate>

</asp:updatepanel>

on c#

for(int i=1;i<=3;i++)
{
(UpdatePanel1.FindControl("txtName_" + i) as TextBox).Text();
}