title: include <x> vs include <x.h>
body: <p>i know we always include a header files, then why do i find some header files like </p>
  
  <pre><code>#include&lt;iostream&gt;
  </code></pre>
  
  <p>with no .h extension but some header files like </p>
  
  <pre><code>#include&lt;windows.h&gt;
  </code></pre>
  
  <p>with the .h extension and i also tried to add.h to some header files like iostream.h but that didnt work, so what's the difference between adding a .h extension when includeing a file andnot doing this.</p>
  
  <p>thanks for all replies... much appreciated</p>