what's the meaning of exit code of program with empty void main()?

I made a simple C program with empty main as given below and compiled it with gcc

int main(){}

upon execution, it return exit code as 25,and if I add a printf statement,after including stdio.h, it returns exit code 5

what's the meaning of 25 and 5 here and why it's being returned by whatever code that is executed before or after main()?exit code is zero if I use int main() and don't put a return statement.