Dear Student,

NDA is only for the 12th passout students not for the bachelors. You can complete your 12th from any stream to participate in NDA exam and if you want to get into Navy And Airforce through NDA then MAths and Physics is must to appear in the exam.

And if you are thing to take admission in B.tech then after completing this degree you can give CDS exam which is also for defence. And to take part in CDS your branch or course doesn't matter, you just need to complete your graduation from any of the course or from any of the branch.

BTW CSE and IT is similar branches so you don't need to worry about the branch if you are getting any of them.

Good Luck k:)