title: tolower() Function not Working in C99
body: <p>I am using the CS50 appliance from Harvard and trying to make a character lowercase. I am trying to use the <code>tolower()</code> function but when I try to use it I get the message <code>implicit declaration of function 'tolower' is invalid in C99</code>. Anyone care to elaborate on why I would be getting this message. I have included <code>stdio.h</code> as well as <code>string.h</code>. </p>