When you register for CS101, you make a committment to put forth your best effort. One expectation is that you will attend class. The lectures do not necessarily follow any book, and you are held accountable for all material covered in class
Some of your grade is based on class participation.
Of course, anyone may need to miss a class a couple of times during the semester, but it is your responsibility to learn what was covered in class. If unavoidable circumstances necessitate an extended absence, you should make arrangements with the instructor as soon as possible, preferably in advance.
Attendance in lab sections is crucial. Your graded labs will be returned in lab sections, and you will have an opportunity to discuss written comments with the TAs during lab. Also, the lab assignments require a demonstration of your working program during the lab section immediately preceding the due date. You must attend your lab section in order to give the required demonstration.