Function operation in cpp version

Hi,

I wonder what the function adding, subtracting, multipying, dividing etc. in cpp form in dolfin?
for instance, I have a function a and function b, and I want to have c=a-b(all in the same functionspace), in python, I can write
c.vector()[:]=a.vector() - b.vector(), but in cpp version, a->vector() is a shared pointer to a’s genericvector and (*a->vector()) - (*b.vector()) will report error when compiling.

Any suggestion would be appreciated!

Yuxiang