title: what difference between while(*p){p++;} ,while (*++p){;} and while(*p++){;}?
body: <p>It's about <code>strcat</code> function.</p>
  
  <pre><code>while (*p)
      p++;
  </code></pre>
  
  <p>and </p>
  
  <pre><code>while (*++p)
      ;
  </code></pre>
  
  <p>both works, but</p>
  
  <pre><code>while (*p++)
      ;
  </code></pre>
  
  <p>does not work. I think first and third should be same, but it's not.</p>