Hello there,
First of all, don't be upset. You can maintain your CGPA, if you do some smart work and some hard work. Both are necessary here. Don't worry, if your 1st semester goes bad. Now its time to focus on further studies.
Now, if its your 2nd semester, then start studying from the very first. Make proper notes, and also follow some good books. Regarding the books, you can ask them from your seniors and from your teachers as well.
Below, I am listing some best books for 1st year CSE students.
Don't go too much deeper in these books. Read only some level above the exam level. It eill be enough for you. Check your previous year question papers for your branch.
See the exam pattern in them, and solve as much problems as you can.
Hope it helps.
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