title: What exactly does fork return?
body: <blockquote>
    <p>On success, the PID of the child
    process is returned in the  parent’s 
    thread  of  execution,  and  a  0  is
           returned  in the child’s thread of execution.</p>
  </blockquote>
  
  <pre><code>p = fork();
  </code></pre>
  
  <p>I'm confused at its manual page,is <code>p</code> equal to <code>0</code> or <code>PID</code>?</p>