All you really need to say is: There are some rules in C which neither the compiler nor the runtime is required to check if you've broken. On the contrary, the

All you really need to say is: There are some rules in C which neither the compiler nor the runtime is required to check if you've broken. On the contrary, the implementation is allowed to assume that you haven't broken them - which means that if you do break these rules, all bets are off as far as the behaviour of your program goes, which may lead to all sorts of strange and apparently inconsistent results.