If you're doing this from scratch (i.e., you're not trying to modify an existing cylinder), I'd recommend using the Revolve tool (i.e., make the profile of the cylinder with the scoop out and revolve it).
Here's a tutorial I made for a tin can than may provide some insight into what I mean:
http://supercoldmilk.com/ac3dtut/beginner/can.html . Instead of making the ridges, just make your cylinder with a "c" shaped scoop for a profile. Let me know if that doesn't makes sense.