What is the err in my code???? Please!!

Question

The program should calculate an add and multyply between two "long number" in string

https://code.sololearn.com/cpCPSnG4zE5Q/?ref=app

Answer 1

Remove the duplicate question.
- https://www.sololearn.com/Discuss/2134440/?ref=app
- https://www.sololearn.com/Discuss/2134441/?ref=app
- https://www.sololearn.com/Discuss/2134442/?ref=app

Answer 2

Convert number to "long" format

Answer 3

https://code.sololearn.com/cpCPSnG4zE5Q/?ref=app