C++ is (mostly) just a superset of C. Some constructs add a bit of overhead but in simple cases this doesn't matter. In "complex" projects, you would be duplicating much of that same functionality anyway in C (complicated data structures, for example), and you'll get identical performance.
I'm not sure what question you posed your lecturer but it is important to note that the language itself doesn't do anything that adds algorithmic complexity. It's really what you do with it that counts. Presumably, your real gripe is with object oriented design methodology, but even then, it's not the objects, it's how you use them
Demul is written in C++ as far as I know, by the way.