title: #ifdef #else #endif macro question
body: <p>I am new to C, and I am maintaining someones code. I came across this in the header file. I can understand that if the source is compiled on the windows it will enter the if statement else if the code is compiled on a linux it will enter the else statement. Correct me if I am wrong.</p>
  
  <p>However, the question is why is # (hash) used in front of all the include headers?</p>
  
  <p>Many thanks for any suggestions,</p>
  
  <pre><code>#ifdef WIN32
  #   include &lt;conio.h&gt;
  #   include &lt;process.h&gt;
  #   include &lt;stdlib.h&gt;
  #   include &lt;string.h&gt;
  #else
  #   include &lt;unistd.h&gt;
  #   include &lt;termio.h&gt;
  #   include &lt;sys/types.h&gt;
  #   include &lt;sys/stat.h&gt;
  #   include &lt;fcntl.h&gt;
  #endif
  </code></pre>