There is no just C and just C++. There are different compilers for different platforms. And with every compiler, it's possible to write anything in such a stupid way killing performance quite well. Having all that, how are you going to compare languages? And if you also remember that you can actually write in C using C++ compiler...
No wonder "people" (those you refere to) "are not providing examples". The statements they made are hardly based on something real. Languages really can be different in performance, but the attempts to compare are usually simply invalid. For comparison, you need to have identical code samples. But if the code is really identical, this means the same language, such as in case of C disguised as C++.
A language that doesn't affect the way you think about programming, is not worth knowing.
—SA