Question 2: Add Two Number

The description of the question can be in the link

https://leetcode.com/problems/add-two-numbers/

1. My code for the question:

Idea: The full idea is clear that we need to take out the number one by one and then do the sum. The first thing needs to be careful is the carry for the number. Next thing we need to be careful is when the last digits are calculated, we need to make sure that there is no extra 1 there to be appended.