Creating a form with calculations

HimanshuS87 are you using Forms or Forms Pro? If Forms Pro you could do something with Microsoft Flow. 

I don't see it being part of one form unfortunately. I think I see it more like this:

FORM QUESTIONS

Question 1 - Event Name/Code - ideally something unique

Question 2 - Choice - Pre Event or Post Event (user selects which one they are completing)

Question 3 - Text - Coke Stock - 10

Question 4 - Text - Sprite Stock - 8

And so on

Then the user fills the same form out again at the end of the event, with everything being filled out and Question 2 being selected as Post Event. If your event name or code is unique and the person completing it is unique, you could do something with the results to add to your SharePoint list.