I don't think there is any built in standard function to do it in C++. You need to use numerical techniques to solve this. Try implementing trapezoidal, simpson etc.. in C++.
The best way is to create your own classes in such situations. It is not difficult to find sample code on the net. Even if you find it, it won't be handy, because your own code can't take the place of someone else's.
I think it is a waste of time to try understanding sample codes written by other people. In stead, you should write your own code. Yeah, it may take more time but, it will be educatinal for you.
thanks for for help. I've programmed a simple runge-kutta function, it's not a good approximation but according to my lecturer it's good enough for this project