What is the true OUTPUT of this code?

Question

According to the C compiler of sololearn app , the answer is 22. when i try this code in another app, i had a answer is 21. which one is the correct one? Is this depend on the compiler?
https://code.sololearn.com/cW4mQ0W12HAd/?ref=app

Answer 1

that is an example of undefined behavior, where the program run in unpredictable way.

for example in you case
++i + ++i + ++i
we dont know when ++i is being executed for the first time.
its all based on compiler implementation on how to handle this (cmiiw) so the result might be different on different compiler