Cygwin error trying to save chars in a string (C)

Question

https://code.sololearn.com/cG2y93uidgE1/#c
I'm struggling with Cygwin exceptions since i started studying C, i have a text file that has 3 characters long lines and i should create a string that contains 3 chars a time and then doing something with it but im having problems from the very beginning as you can see. I'm working on windows not on sololearn playground.

Answer 1

what's the difference between a simple while and a do-while?