title: int? maxResults what does the ? means in this statement
body: <blockquote>
    <p><strong>Possible Duplicate:</strong><br>
    <a href="https://stackoverflow.com/questions/2699373/c-sharp-basic-question-what-is">C# - Basic question: What is ‘?’?</a>  </p>
  </blockquote>
  
  
  
  <p>I have found this statement in a function arguments.</p>
  
  <pre><code>public static SyndicationFeed GetDataFeed(...... int? maxResults)
  </code></pre>
  
  <p>what does that means?</p>