Hi roshan ,
You can never become a programmer after completing your mechanical degree , but you can do this when you are pursuing your mechanical course
I Personally feel that programming should be everyones second priority as now a days even mechanical engineering require programming when it comes to automation .

So just start learning from now you have to master atleast 3 languages I would suggest you go for C++, java and python after that go for data structure and algorithms .

Hope it helps!!!

Nowadays mass recruiters hire Street genius from any discipline in there companies so so you can try to get into one to learn programming you can go to websites like udemy, W3Schools and other websites like stackexchange etc to begin your programming journey

hello roshan,

here  is the brief explanation for you here

Learn a language used professionally (like Ruby or C#; do research on how different languages are used, how popular they are commercially, ... and then go from there).
After that, practice for a couple years (the length depends on you individually) by making small programs for yourself, contributing to open-source (that'll probably come towards the end), and just generally build your resume.
Do a lot of reading from those who know a lot more than you (like Spolsky or Atwood, for example). Read about advanced features of your chosen language (a ton of resources online for that).
Read the seminal books of the field (like SICP, Code Complete, ..., and possibly TAOCP).
Learn another language if you have time, but don't mistake quantity for quality.
Finally, a college degree in computer science/engineering or other such formal education is VERY helpful in terms of both learning important concepts and also looking more qualified to employers.