title: Can I modify a passed method parameter
body: <p>my gut feeling says I shouldn't do the following. I don't get any warnings about it.</p>
  
  <pre><code>void test(DateTime d)
  {
   d = d.AddDays(2);
  //do some thing with d
   }
  </code></pre>
  
  <p>or is this more proper</p>
  
  <pre><code> void test(DateTime d)
   {
   DateTime _d = d.AddDays(1);
  //do some thing with _d
   }
  </code></pre>
  
  <p>For some reason I have always handled passed parameters like in the second example.
  But I am not sure if it's really nessesry...maybe it's just unnessary code.</p>
  
  <p>I am not thinking that the calling method would be using the modified value.
  anyone have any opinions</p>