title: Why do we use NULL in strtok()?
body: <p>Why do we use <code>NULL</code> in <code>strok()</code> function?</p>
  <pre><code>while (h != NULL)
  {
      h = strtok(NULL, delim);  
      if (hold != NULL) 
        printf(&quot;%s&quot;, hold);    
  }
  </code></pre>
  <p>What does this program do when <code>*h</code> is pointing to a string?</p>