Excellent, so that's a new C++11 function? Good to know; thanks for posting that!
I'm sorry, I mixed up that funtion. What I meant was std::to_string.
Dev C++ is an IDE, it uses MinGW as the compiler, and MinGW's C++ library implements the standard. Though the version of MinGW that ships with Dev C++ is probably outdated.
Also, I'm not sure if DevC++ even supports std::stringstream?
Still, I recommend QtCreator over Dev C++.