The code you write in the Arduino environment is C/C++. Simple as that. It just comes with a bunch of predefined functions and libraries to make everything easier. All the code is there if you want to look at it. The projects that are created all have cpp files somewhere in the project folder. All the Arduino environment does is refrain from displaying some of the #includes and the main function of the project's code... so it's all there, just not explicitly in Arduino.
You can still compile all the sketches from outside arduino using the avr-gcc tools and rot from the command line, or with makefiles.