Not understanding logic !

Question

https://code.sololearn.com/cs968l7G5v6V/?ref=app

In this program, I want to know why when the years are same and m2 is less than m1 , y don't return -1.

I mean m2<m1
So, 12 is added to M2
Then 1 is subtracted from y2 i.e. when y1= y2 (eg. Both are 2020), y2 becomes 2020 - 1 = 2019
Now, y = y2 - y1
=> y = 2019 - 2020 = -1
This is my logic but the program is okay (works fine)

https://overiq.com/c-examples/c-program-to-calculate-the-difference-of-two-dates-in-years-months-and-days/

Answer 1

It's always giving some junk no. On inputting same year so it does work fine