How to use fflush(stdout)

I want to know how to use fflush(stdout) as I haven’t used this before and I am facing problem.can anyone please give a sample code to use it.
in june challenge one has to use it in solving DARTS501 …question is asking to clear output buffer each time after printing a line.

As far as fflush(stdout) is concerned.its simply flush(stdout); thats it .