title: Proper usage of #if directive in C?
body: <p>The following structure for C preprocessor directive <code>#if</code> works well.</p>
  <pre><code>#define C  1
  
  #if C==1
  ...
  #endif
  </code></pre>
  <p>But I'd like to use something like this:</p>
  <pre><code>#define REAL double
  
  #if REAL==double
  ...
  #elif REAL==float
  ...
  #else
     assert(0);
  #endif
  </code></pre>
  <p>It's not valid. Is there a solution?</p>