title: update textbox when changed without refreshing
body: <p>I'm working on my own aspx program and now i have a calculator which i want to be able to fill in some values and when you press tab to the next value and fill it in it will automatically calculate and write it into a textbox(or label). this must be without having to refresh the page.
  would this be possible in combination with c# or would i need to look for php + ajax to get this done?</p>
  
  <p>i had the following coded:</p>
  
  <pre><code>&lt;asp:TextBox ID="tbx_rms" onchanged="textboxcalc" runat="server"&gt;&lt;/asp:TextBox&gt;
  &lt;asp:TextBox ID="tbx_volt" onchanged="textboxcalc" runat="server"&gt;&lt;/asp:TextBox&gt;
  &lt;asp:TextBox ID="tbx_anw1" Enabled="false" runat="server"&gt;&lt;/asp:TextBox&gt;
  &lt;asp:TextBox ID="tbx_anw2" Enabled="false" runat="server"&gt;&lt;/asp:TextBox&gt;
  &lt;asp:TextBox ID="tbx_eff" onchanged="textboxcalc" runat="server"&gt;&lt;/asp:TextBox&gt;    
  &lt;asp:TextBox ID="tbx_anw3" Enabled="false"  runat="server"&gt;&lt;/asp:TextBox&gt;
  </code></pre>
  
  <p>and this is the c# code:</p>
  
  <pre><code>public void textboxcalc(object sender, EventArgs e)
      {
          if (tbx_rms.Text != "" &amp;&amp; tbx_volt.Text != "")
          {
              double rms = Convert.ToDouble(tbx_rms.Text);
              double volt = Convert.ToDouble(tbx_volt.Text);
              double ant = Convert.ToDouble(rms / volt);
              if (tbx_eff.Text != "")
              {
                  double effi = Convert.ToDouble(tbx_eff.Text);
                  double tot = Convert.ToDouble((effi / ant) * 100);
                  tbx_anw3.Text = Convert.ToString(tot);
              }
              tbx_anw1.Text = Convert.ToString(ant);
              tbx_anw2.Text = Convert.ToString(ant);
  
          }
  </code></pre>
  
  <p>I hope it is clear enough what my intentions are and if not i will happily answer any questions.</p>