Yes smoking a pack of cigarettes a day is bad for your health and lungs.
Even smoking one cigarette per day is bad as the more you smoke the more damage you do to your lungs and for every pack of cigarettes you smoke you shorten your life by at least a week or two.
Smoking a pack of cigarettes per day all year can shorten your life by 1 to 3 years.
The longer and more you smoke the shorter your lifespan is likely to be.
So the best thing to do is never smoke.
I had an aunt who smoked a pack of cigarettes per day since she was 18 years old and she died about 3 years ago of lung cancer and breathing problems at the age of 64.
She was very short on breath and was using an oxygen tank and was still smoking until she went to the hospital and was on life support for a week before she died.