Why we use return 0;?

Answer 1

the result of the function is 0.

Sometimes it's used on main, because the function is defined "int main", so its mean that you have to return a numerical value. (else, It will say error).

You can make the main void, and delete or comment the return statment-

Answer 2

listen to Nahuel he knows

Answer 3

you can change the code to int main(void)