title: strtok() - Why you have to pass the NULL pointer in order to get the next token in the string?
body: <p>This is the explanation of strtok().</p>
  
  <pre><code>#include &lt;string.h&gt;
  char* strtok( char* s1, 
                const char* s2 );*
  </code></pre>
  
  <blockquote>
    <p>The first call to strtok() returns a pointer to the first token in the
    string pointed to by s1. Subsequent calls to strtok() must pass a NULL
    pointer as the first argument, in order to get the next token in the
    string.</p>
  </blockquote>
  
  <p>But I don't know, why you have to pass the NULL pointer in order to get the next token in the string. I searched about 15 minutes, but didn't find an explanation in the internet.</p>