For the case study questions you shold know the exact behavior of the system (smart card readers, messaging behaviors) because assumptions and therefore the inferences on theses assumptions may be incorrect (even if they are coherent) and they are not accepted. So you should either really increase your domain knowledge beforehand if you do not have, or it is a chance for you if you are already working on these areas. I was working more on radars and related systems so this was a huge disadvantage for me. As for the programming questions, take great care of the completeness, This is what is asked, I mean do not think just related code lines would work. No it won't. For each subquestion, think of it as the whole application program and code every bit of it. (The related variables, initiations etc.) And think of algorithm optimizations because this is also asked. Finaly that d bag I mentioned, may come up with general opinions about your whole qualifications based on the some incorrect parts of the answers or assumptions you provided, which I think is so unfair, in this case do not bother him. :)