In my answer to the question Determine missing number in data stream I have a comment which indicates C++ is not a valid form of pseudo-code. Lacking a formal definition of what pseudo-code actually is I don't see how specified languages can be excluded.
C++ is defined in terms of a series of objects and operations working on an abstract machine. The meaning of the code is unambiguous. Indeed, the syntax of C, on which C++ is based, is often used as the basis of pseudo-code, so it can't be entirely incorrect to use such syntax.
The argument was made that somebody who doesn't know C++ wouldn't understand the answer. Is this not true of absolutely any language, even pseudo code? If I choose to answer in nothing but a series of set operations, one would have to be well versed in those to understand. If I chose to answer with any formal language you'd also have to be versed in that to understand. That is, regardless of how I answer the question, somebody would have to understand that language to be able to understand the answer.