title: implicit declaration of function itoa is invalid in c99
body: <p>When I try use the function <code>itoa()</code>, I get the warning:</p>
  
  <blockquote>
    <p>implicit declaration of function  is invalid in c99.</p>
  </blockquote>
  
  <p>I have included stdlib.h on my header. I'm trying to call this function inside a function, I'm not sure if this is allowed.</p>