Зачем нам возвращать 0 в C?
The return value is the exit code of your program, the shell (or any other
application that ran it) can read and use it.
The 0 exit code is a widely accepted convention for 'OK the program execution
was successfull'. And for non-zero numbers, it conventionally means the
program didn't execute successfully or there is an error.
Heckar