title: Header should be included once
body: <p>In header files I've seen two main ways for defining macro to avoid including the file more than once.</p>
  
  <p>1.</p>
  
  <pre><code>#ifndef SOME_CLASS
  #define SOME_CLASS
  //code ...
  #endif
  </code></pre>
  
  <p>2.</p>
  
  <pre><code>#ifndef SOME_CLASS
  //code...
  #define SOME_CLASS
  #endif
  </code></pre>
  
  <p>Which is more preferable and why?</p>