I had read somewhere, i think in my college on a pamphlet, that if someone has taken CPT then he cannot apply for OPT. Is this true?

Immigration service (USCIS) approval is not required-CPT is approved in
our ISP office. You can do up to 364 days of CPT without affecting your
eligibility for OPT (Optional Practical Training.) However, if you do
365 days or more of CPT, you will lose your eligibility for OPT.

src:http://www.highline.edu/stuserv/international/thunderworld/optCpt.htm

is it necessary to have a job offer before we apply for CPT? Do we have to enroll for classes while on CPT?

Is it necessary to have a job offer before we apply for CPT?
-Yes
Do we have to enroll for classes while on CPT?



- Not in summer.
For other semesters you might have to ask your international advisor.