What does mean .h

[Medet Kozhabaev]

what is the difference between iostream and iostream.h?

[Cubbi]

iostream is the name of one of the header files in the C++ standard library. Its contents are fixed by the standard to be exactly http://en.cppreference.com/w/cpp/header/iostream

iostream.h is the name of a header file used in some pre-1998 non-standard dialects of early C++. Its contents vary between historic compilers that provided it.