Hello saurabh.

Both computer science and mechanical engineering are totally different streams.

It's you who  have to choose what makes your interest.

Both have good demand for the course.

If you choose computers. You can go with lot of opportunities based on software,coding, scripts, database management...etc.

When comes to mechanical engineering.you have a great scope of developing new machinery. And mechanical also deals with robotics,so u can choose career in robotics industry by mechanical engineering also.

Hope you choose wisely 

Any more questions feel free to ask us.