Living in YYC sans car is do-able, but obviously it will be limiting. Calgary is bigger than you may think so getting from one end of town to the other without a car may take planning and time.
I say this next part respectfully. YYC always reminds me of an American city in that the downtown is mostly offices and people for the most part seem to live out in the burbs. To me, downtown YYC after working hours seems very deserted. (I'm talking specifically the area from Eau Claire Market over towards the Fairmont.)
I hasten to add that YYC is very safe, like pretty much any other Canadian city. It's just that the downtown seems to lack a certain vibrancy. The usual conveniences are there though and the +15s are a great way to get around once you figure out which way is which. In terms of car rental there's an Avis right downtown and there is at least one
car sharing program too.
I do have to say that YYC is a lovely place and I'm forever envious of people who live there as the proximity to Banff is almost reason enough to move there.