title: Asp.net adding parameter to url string
body: <p>I'm displaying a list of filtered items in a page, and now I have to limit the displaying by paginating the results.</p>
  
  <p>So if I have url parameters like these: </p>
  
  <pre><code>example.com/?category=pizza&amp;period=today
  </code></pre>
  
  <p>where both category and period can also not being showed:</p>
  
  <pre><code>example.com/?period=today
  
  example.com/
  </code></pre>
  
  <p>how can I add a "Next page" in the end that keeps any previous parameter and adds</p>
  
  <pre><code>&amp;pagenum=5 
  </code></pre>
  
  <p>or if there are no parameters:</p>
  
  <pre><code>?pagenum=5
  </code></pre>
  
  <p>Tnx in advance!</p>