Hey Mate #-Link-Snipped-# ,
I don't have deep knowledge of the CDAC colleges and course, so someone from this community will answer your second question i.e. " Which course and college should be better for me ? Please give me preferences of college and courses ".
I WILL ANSWER YOUR - " Is their any problem in placement due to 4 year gap ? " QUESTION.
Hope you will get some light from it.
I wont give you false advice or suggestion or comment that you will get job easily by doing cdac but I will tell you the truth. Its not very easy to justify 4 years gap. Everytime you face an interview this question will be presented to you.Â
You have to tackle this very cleverly.Whatever you say the interview panel should get satisfied with it.If yes, you will be lucky:)
Also most of the companies have shortlisting criteria  based on year of passing out, cutoff percentage and stream. So its likely that you will be presented with less opportunity.Â
Whatever opportunity you get through cdac you have to crack it.
Along with that you need to -
1.be technically very strong
2. be honest in all questions in interview
I wish you all the best for your future. Do study hard and go crack it !