I have been smoking for a while now, i started when i was 15 and i want to quit. but how will it affect my workouts?

my old room mate quit and gained almost 35 lbs of fat in 2 months. i dont want that.

I have gone from a pack a day, to about 6 a day. not too long before i go cold turkey.

any input/suggestions would be appreciated.

Zac