Wow... this is a good one (conversation, I mean).
You weren't very specific when you referred to designing weapons, so everyone (including me, initially) assumed you were talking about firearms and such. However, you are a computer engineering student, correct? In India. I don't know much about the Indian military system but am intimately familiar with the American one (having been a member and then civilian employee since 1997). In the States, if you join the military to pay for school, you really have to be a soldier first and then worry about being a student after you're done. I deployed four times, and am currently 10,500 km from home on another overseas tour... there isn't the kind of stability that one really needs to have to buckle down on an engineering degree.
All of that being said... is it advanced weapons systems that you're referring to? If so, continue your studies in computer engineering and find a mentor who knows what's going on (this is where the Army officers come in, perhaps) so that they can direct you.