If the question had been tagged c, your code block would have worked. But, it wasn't.
You could add the tag, I suppose... But that seems lame, since the question wasn't about C.
So your next best option is to simply force syntax highlighting for your code block, by prefixing it with a special comment:
<!-- language: lang-c -->
... code goes here, indented by four spaces as usual ...
I've done this for you. Enjoy!