gistfile1.cs

    [ToolboxItemAttribute(false)]
    public class PowWebPart : WebPart
    {
        protected TextBox txtX;
        protected TextBox txtY;
        protected Button btnCalc;
        protected Label lblResult;

        protected override void CreateChildControls()
        {
            txtX = new TextBox();
            Controls.Add(txtX);

            txtY = new TextBox();
            Controls.Add(txtY);

            btnCalc = new Button();
            btnCalc.Text = "Calculer";
            btnCalc.Click += btnCalc_Click;
            Controls.Add(btnCalc);

            lblResult = new Label();
            Controls.Add(lblResult);
        }

        protected override void RenderContents(HtmlTextWriter writer)
        {
            EnsureChildControls();
            writer.AddAttribute(HtmlTextWriterAttribute.For, txtX.ClientID);
            writer.RenderBeginTag(HtmlTextWriterTag.Label);
            writer.Write("X");
            txtX.RenderControl(writer);
            writer.RenderEndTag(); // Label
            writer.Write("<br/>");

            writer.AddAttribute(HtmlTextWriterAttribute.For, txtY.ClientID);
            writer.RenderBeginTag(HtmlTextWriterTag.Label);
            writer.Write("Y");
            txtY.RenderControl(writer);
            writer.RenderEndTag(); // Label
            writer.Write("<br/>");

            btnCalc.RenderControl(writer);
            writer.Write("<br/>");

            lblResult.RenderControl(writer);
        }

        private void btnCalc_Click(object sender, EventArgs e)
        {
            int x;
            int y;
            if (int.TryParse(txtX.Text, out x) && int.TryParse(txtY.Text, out y))
            {
                lblResult.Text = Math.Pow(x, y).ToString();
            }
            else
            {
                lblResult.Text = "Nombres invalides";
            }
        }
    }