The definition void main() { /* ... */ } is not and never has been C++, nor has it even been C. See the ISO C++ standard 3.6.1[2] or the ISO C standard 5.1.2.2.1. A conforming implementation accepts
int main() { /* ... */ } and
int main(int argc, char* argv[]) { /* ... */ } A conforming implementation may provide more versions of main(), but they must all have return type int.

The int returned by main() is a way for a program to return a value to "the system" that invokes it. On systems that doesn't provide such a facility the return value is ignored, but that doesn't make "void main()" legal C++ or legal C. Even if your compiler accepts "void main()" avoid it, or risk being considered ignorant by C and C++ programmers.