We were given a C (C++ in fact) code and that was all. Of course, my first idea was to start reading that cryptic code, deciphering its loops and so on.
Sometime during the contest the admin posted this hint:
    HINT: It's much more than just a C program 
So, could it be something other than a C program? Let's see. The first thing that caught my C-eyes was that identation... sends shivers down the spine. Now wait a minute! Look at the whitespaces. It reminds me that esolang, *Whitespace*!
And that was it indeed. The code was in the whitespaces, not the proper characters themselves. Using this interpreter http://ws2js.luilak.net/interpreter.html we got the flag.
    the_flag_is_WpUAItsadmhak