title: while(foo) vs while(foo != NULL)
body: <p>Can someone explain how <code>while(foo)</code> vs <code>while(foo != NULL)</code> are equivalent? Also:</p>
  
  <p><code>while(!foo)</code> vs <code>while(foo == NULL)</code></p>
  
  <p>I know that ! is not, but that is about all I know.</p>