Hello Ashish Mishra,

You can go for BCA directly after 12th standard as it is a bachelor degree in computer.  A large number of college admit student on the basis of 12th marks. But some reputed college conduct an entrance exam for admission like GGSIPU , the one institute that conduct thier own test. 

So, it depend on you that which college suits you the most so analyse it and go for further processes.

Hope it helps.

Thank you :)