proč potřebujeme vrátit 0 v 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.
proč tam je return 0 použity v c
The return value of main() becomes the exit status of the process.
Traditionally, an exit status of zero usually means “OK,”
while any non-zero value indicates some kind of error.
This is analogous with how many system calls likewise return zero
or an error code.