ASP.NET

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace StudioLibrary_8707
{
    [DefaultProperty("Text")]
    [ToolboxData("<{0}:MathBox2 runat=server></{0}:MathBox2>")]
    [DefaultEvent("Click")]
    public class MathBox2 : WebControl
    {
        TextBox txtMath = new TextBox();
        Button butSum = new Button();
        Label lblResult = new Label();

        [DefaultValue("0")] 
        public string Text 
{
    get
    {
        // Make sure child controls exist.
        EnsureChildControls();
        // Return the text in the TextBox control.
        return txtMath.Text;
    }

    set
    {
        // Make sure child controls exist.
        EnsureChildControls();
        // Set the text in the TextBox control.
        txtMath.Text = value;
    }
}
        // Declare the event.
        public event EventHandler Click;

        protected virtual void OnClick(EventArgs e)
        {
            if (Click != null)
                // Raise the event.
                Click(this, e);
        }


        char[] strSep = {'\r'};

        public string[] Values
{
    get
    {
        EnsureChildControls();
        // Return an array of strings from the TextBox.
        return txtMath.Text.Split(strSep);
    }
    set
    {
        EnsureChildControls();
        // Set the text in the TextBox from an array.
        txtMath.Text = String.Join(" ", value);
    }
}

        public string Result
{
    get
    {
         EnsureChildControls();
         // Return the result from the Label.
         return lblResult.Text;
    }
}

        public void Sum()
{
    EnsureChildControls();
    // If there is text in the TextBox.
    if (txtMath.Text.Length != 0)
    {
        // Break the text into an array, line by line.
        string[] arrNums;
        arrNums = txtMath.Text.Split(strSep);
        double dblSum = 0;
        // Add each element in the array together.
        foreach (string strCount in arrNums)
        {
            // Use error handling to 
            // ignore non-number entries.
            try
            {
                dblSum += Convert.ToDouble(strCount);
            }
            catch
            {
            }
        }
        // Display the result in the label.
        lblResult.Text = dblSum.ToString();
    }
    else
        lblResult.Text = "0";
    }

        protected override void CreateChildControls()
        {
            // Add the sub controls to this composite control.
            // Set the TextMode property and add textbox.
            txtMath.TextMode = TextBoxMode.MultiLine;
            Controls.Add(txtMath);
            // Start a new line
            Controls.Add(new LiteralControl("<br>"));
            // Set the Text property and add the Button control.
            butSum.Text = "Sum";
            Controls.Add(butSum);
            // Add Label and Literals to display result.
            Controls.Add(new LiteralControl("&nbsp&nbspResult:&nbsp<b>"));
            Controls.Add(lblResult);
            Controls.Add(new LiteralControl("</b>"));
            // Add event handler.
            butSum.Click += new EventHandler(butSumClicked);
        }

        void butSumClicked(object sender, EventArgs e)
        {
            // Call the Sum method.
            Sum();
            // Call the event method.
            OnClick(EventArgs.Empty);
        }
        protected override void RenderContents(HtmlTextWriter output)
        {
            EnsureChildControls();
            // Render the control.
            base.RenderContents(output);
        }
    }
}

    <assemblies>
            ...
            <add assembly="StudioLibrary_8707, Version=1.0.0.0, Culture=neutral"></add>
    </assemblies>
<controls>
          ...
          <add tagprefix="Lib" namespace="StudioLibrary_8707" assembly="StudioLibrary_8707, Version=1.0.0.0, Culture=neutral">
</add></controls>

<lib:mathbox2 id="MathBox1" runat="server" onclick="MathBox1_Click" xmlns:lib="#unknown" />