Accounting & Commerce

You can pursue courses like CA, CS, and ICWA along with your B.Com.

You should opt for B.Com.

Yes, you can switch your career to computers field from commerce stream. There are a lot of PG courses available after class 12th with commerce stream that you can pursue. Some of the courses comprise:
MCA
PGDCA

SET or NET organize regular test at national level every year. To appear for this exam, you need to have following:
(a) Graduation in 1st class
(b) Minimum 55% to 60% aggregate marks in M.Com.
For more details, follow their respective websites.

Along with CMA, you need to learn basic applications of computer. Read your computer syllabus carefully from the given prospectus. According to it, try to pursue Diploma in computer application in finance and accounts like ADCA (one year) from a recognized training institute.

If you are interested to get a job in different companies then try to pursue following courses along with B.Com as
(a) ADCA in finance and accounts from recognised training institutes.
(b) CAT i.e. certificate in account technitian from ICWAI or ICMAI.
If not then you can start your preparation for Bank PO, SSC etc. to get jobs in government sector.
(c) If you want to continue your study, then you may pursue different courses like M.Com, MBA, CA orCMA (ICWAI).

You can go for BCA, B.sSc in IT, software system, computer science and computer technology. Also, since you have maths, you are also eligible for B.Arch.

You can go for either AICTE or UGC affiliated universities.