Hello,

Btech is a degree and domain like mobile computing or cloud computing is specialization. if you want to pursue specialization then during your course you may have specialized subject in parts or set or either is section. By the end of course duration, you will have complete knowledge about your domain.

Cloud computing and mobile computing basic concept is same. Cloud is a virtual storage provided by different product based companies like Amazon-AWS, IBM cloud, Microsoft Azure. There are many providers.

Hope it helps!