There is no such [standard] graphics.h library in either C or C++. If you have it on your machine, it's likely a non-standard lib that comes bundled with your compiler/IDE. (And from the sound of it, you are using something very, very outdated)
Practically anything that works in C will also work in C++, so if you want you can continue to use graphics.h with cpp (assuming you have it).
Otherwise there are many other libs available on the interwebs that make graphic output easier.
If you're looking to make a game, check out SFML.
If you're looking to make a widgetry program (like with pushbuttons, forms, etc), check out Qt and/or wxWidgets.
All those libs are likely to be found on the first hit in Google.