I am developing an desktop based application in c++. I want to make it touch screen enabled, where touch screen is available. My question do I need a separate version for this application for touchscreen?
If you are planning on adding specialized support for touchscreens, like multitouch, and enable gestures for your application, you'll have some separate code handling that. If not, whatever OS you are using, assuming your code is portable, mouse input should be equivalent to touch input.
That being said, your question is quite vague, I'm not sure if my answer is what you expected.