I need to be able to format a decimal into a string with a specified number of decimal places.

Here is my simple test page code consisting of a a text box, a button and a label. The idea is for the user to enter a decimal number, i.e., 23.345456, then click the button and have the label show the formatted decimal string. But try as I may, I cannot get it to work.

Code:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="DecimalFormat.aspx.cs" Inherits="DecimalFormat" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
    <style type="text/css">
        .style1
        {
            font-size: large;
            color: #000080;
            font-weight: bold;
            font-family: Arial, Helvetica, sans-serif;
        }
        .style2
        {
            font-family: Arial, Helvetica, sans-serif;
            font-weight: bold;
            font-size: medium;
            color: #000080;
        }
    </style>
</head>
<body>
    <form id="form1" runat="server">
    <p class="style1">
        TEST DECIMAL FORMAT USING C#</p>
    <div>
    
        <span class="style2">Enter Decimal</span> :<asp:TextBox ID="txtBoxDecimal" 
            runat="server"></asp:TextBox>
        <br />
    
    </div>
    <asp:Button ID="btnFormat" runat="server" Text="Format" 
        onclick="btnFormat_Click" />
&nbsp;
    <asp:Label ID="labelDecimal" runat="server" Font-Bold="True" Font-Names="Arial" 
        Font-Size="Medium"></asp:Label>
    </form>
</body>
</html>
And here is the underlying C# code:
Code:
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Globalization;         // NumberFormatInfo class

public partial class DecimalFormat : System.Web.UI.Page
{
    public String sDecimal;
    public Decimal decnum;
    protected void Page_Load(object sender, EventArgs e)
    {
        NumberFormatInfo nfi = new CultureInfo("en-US", false).NumberFormat;
        nfi.NumberDecimalDigits = 3;
        //sDecimal = txtBoxDecimal.ToString();
        sDecimal = txtBoxDecimal.Text;
       // decnum = txtBoxDecimal.
        decnum = Convert.ToDecimal(sDecimal, nfi);
    }
    protected void btnFormat_Click(object sender, EventArgs e)
    {
        NumberFormatInfo nfi = new CultureInfo("en-US", false).NumberFormat;
        nfi.NumberDecimalDigits = 0;

        String sFormatDecimal = Convert.ToString(decnum, nfi);
        labelDecimal.Text = sFormatDecimal;
    }
}
Appreciate info on how to do this correctly. Thanks.