CDS eligibility varies for different branches under CDS exam.

But for all branches- IMA. and Officers’ Training Academy, Indian Naval Academy, Air Force Academy minimum educational requirement is graduation.

Therefore graduation degree is must. 

CDS eligibility in detail you can check here.

Hello

NDA exam is one of the very popular exam to join defense forces after 12th class. There are many books available in market but its very important to choose correct books for the preparations. A list of all the important books for NDA exam is given below.
Mathematics

• Pathfinder

CDS (I) updates will be released on 8th-Nov-2017, last date for receipt of Application forms is 4th December 2017 and the exam will be held on 4th-Feb-2018. To know the complete schedule of UPSC exam, you can go through the below link -

UPSC Exam Calender

Hope this helps!!!

You can follow below books for your preparation

English

1. Word Power Made Easy, Norman Lewis

2. Wren & Martin

Mathematics

1-Mathematics for C.D.S. by R.S. Aggarwal

2-Quantitative Aptitude for Competitive Examinations by R.S. Aggarwal.

GK

1- For GK you can start reading newspapers. The Hindu and Indian Express is

Yes, If you are interested in Armed force after B.tech then you can go for TGC (Technical Graduate Course) Entry for which you can apply Twice in a year or
SSC-Tech Entry which also you can apply twice in a year.

TGC Eligibility

Education Qualification: You should have passed the

Yes,you need to complete your Graduate degree course and Intermediate examination with maths and Physics as a compulsory subjects. But you are from commerce background, so you are only eligible to apply for Indian Army/Indian Military academy.

If you are Interested to Join Indian military academy then you can apply

CDS Academic Qualification For I.M.A. and Officers Training Academy graduate in any discipline from any recognised university or equivalent. For Indian Naval Academy: Degree in Engineering from an Institution/University recognized by the central government.
For Air Force Academy: Graduation degree from any recognized university (with physics and mathematics compulsory at

You can only apply for Officers’ Training Academy (OTA SSC Women Non-Technical Course) under CDS as the eligibility criteria mentioned below - Age: Must be born not before July 2, 1992 and not later than July, 1998

Sex: Unmarried women and issueless widows

For more information, you can go through