Why do some includes need the .h and others not? [duplicate]

Answer 1

It's simply the name of the actual file on disk. There is (probably) no file called map.h or stdio in your standard include directory.

The C++ standard library moved away from the previous style of using .h toward not having .h at the end of the file names. This may possibly have been related to making the syntax look more like templates:

#include

vector v;

^{(Preemptive comment: Yes, I know the above needs std:: to build, but it's just an illustration.)}