In pre-standard C++, the prototype of main() didn’t have a return value. On some compilers, it was:

   main() /* no explicit return value; int assumed*/

While others used one of the following:

   int main()  void main()

This chaotic situation was changed recently. Now the Standard specifies the following form:

   int main()

Although most compilers still accept void as a return value, this is an obsolescent feature. You should always use the following form:

   int main()