Adding a faculty as a co-author I and two other student, did a course project and it has been accepted for publication in an international conference. I am confused now that whether I should add his name as a co-author or acknowledge him in acknowledgements ?
I would like to share that though, the entire implementation and writing the paper was done by us, we were student of his class and the work was produced as a part of course project. 

My field is Computer Science.

Edit: As F'x suggests, that I should ask the instructor. What would be an appropriate way to do so given that his name was not added as co-author before acceptance.(We were confident about the work but were not sure about the acceptance. The conference management software was EDAS and it spams email of all co-authors which we wanted to avoid in his case)
Regarding “given that his name was not added as co-author before acceptance”: ask him ASAP. Be honest, be apologetic, explain clearly the situation and the reasons you did not want to add his name beforehand, but also be very clear that you realize now it was a mistake not to discuss it at the time, and that you made the mistake due to your lack of experience in academic publishing.