When replacing the ignition lock cylinder and not the whole assembly, do I still need to get the key programed?

Okay, I bought a new ignition lock cylinder with the key. When I change the cylinder and not the whole assembly. Do I still need to get the key programed? Okay I changed the ignition lock cylinder and the car keeps digging but the key won't turn. I read that after market cylinders don't meet flush so the right stuff isn't connecting to tell my car to run. So I'm assuming I need to get the whole assembly instead. So my question is if I get the whole assembly with the coded key once I change it do I have to get anything reprogramed or will my car just start normal again?