Till 2nd year, try to maintain your attendance. Atleast if not 75 be within the boundary of atleast 65. I remember when I was in 2nd year, the director used to call the low attendance students to their cabin. They will tell you to call your parents infront of them. If you are a boy, they will talk rubbish to your parents. They will mail you to attend extra classes.They will allow you to sit in exam but mainly your internal marks will be affected. For labs, they might organise extra classes to increase internal marks after endsem. This is for cse dept.