I checked division by zero initially, but then realised that 1/0 causes double to represent inf. Thought that this could be useful(?) in some situations. For example, atan(1/0) --> 1.57... instead of error.
Obviously, bc is much more capable than calc. However, calc was not created to replace or even compete with bc or any other awesome command-line calculators. calc is my way of learning a bunch of stuffs (shunting yard).