title: Cannot implicity convert type 'double' to 'string'
body: <p>I am making a program to take the radius of a circle and output the diameter, area, and circumference. I'm trying to start with the diameter, but I keep receiving the error: Cannot implicitly convert type 'double' to 'string.' I've done similar programs using integers, but I can't figure out for the life of me, how to receive floats in text boxes and calculate them so I can output them. This is my code so far.</p>
  
  <pre><code>&lt;%@ Page Language="C#" %&gt;
  &lt;!DOCTYPE html&gt;
  &lt;script runat="server"&gt;
   protected void Button1_Click(object sender, EventArgs e)
   {
   double pi = 3.14159;
   lblDiameter.Text = (double.Parse(radius.Text)) * (double.Parse(radius.Text));
   } 
  &lt;/script&gt;
  
  &lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
  &lt;head id="Head1" runat="server"&gt;
   &lt;title&gt;Circles&lt;/title&gt;
  &lt;/head&gt;
  
  &lt;body&gt;
  &lt;form id="form1" runat="server"&gt;
      &lt;div&gt;
      &lt;asp:TextBox
      id="radius"
       Runat="server" /&gt; 
      &lt;br /&gt; 
  
      &lt;asp:Button
      id="Button1"
      Text="Calculate"
      OnClick="Button1_Click" 
      Runat="server" /&gt;
  
      &lt;asp:Label
      id="lblDiameter"
      Runat="server" /&gt;
  &lt;/div&gt;
  &lt;/form&gt;
  &lt;/body&gt;
  &lt;/html&gt; 
  </code></pre>
  
  <p>Where am I going wrong?</p>