Is there any thing that can be done by c can't be done by C++?
No.
It is incorrect answer because C++ is based on the C89 Standard while C is based on the C99 Standard. So there are things that can be done by C and can not be done by C++. Consider, for example, definitions of arrays with non-const expression for array sizes.
I interpreted his question to be "is there anything you can do with C that you cannot do with C++?", to which the answer is no.
Vlad has interpreted his question to be "is all C syntax also correct C++ syntax?", which is a different question.
Everything you can do with C, you can also do with C++; ultimately, you can just write assembler directly into C++, so you can make the processor do anything that you like.