Does nicotine increase metabolism? so will i for sure gain if i quit smoking? what if i work out?

Exercise will help: Tobacco lowers appetite and raises heart rate, in a way increases metabolism. It also increases blood pressure and has negative effects on blood vessels, so your overall health risk goes up. Exercise is a perfect antidote - it works against weight gain, helps fight sugar cravings that happen after quitting, and reduce desire to smoke. Have low-cal snacks, use nicotine gum/lozenges if needed.

Not for sure, but: Smoking causes many more problems then obesity. Exercise is very good along with proper diet. Check out dash diet1.