If I score 200/360 in this year's Jee main exam, will I be able to do computer science engineering in any of NIT's or IIT's?

Yes, 200 is a decent score to get admission in NITs. At this mark your expected rank will be around 6000. There are total 31 NITs with 18K seats & NIT admission depends on home state quota and category also with JEE Main rank. if you want to get CSE branch in top NITs like Warangal, Surathkal, Tirruchirappalli, Calicut, Delhi, Jaipur Etc. your marks should be more than 220.

To check which NITs and branches you can get based on your expected rank you can use below college predictor.

Click on the below link-

http://www.engineering.careers360.com/jee-main-college-predictor

IITs admission is based on JEE Advanced exam.