C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 29:
[29.3] Should I use void main() or int main()?

int main()

main() must return int. Not void, not bool, not float. int. Just int, nothing but int, only int.

Some compilers accept void main(), but that is non-standard and shouldn't be used. Instead use int main().

void main()  //  BAD; DO NOT DO THIS
{
  ...
}
int main()  //  GOOD
{
  ...
}
int main(int argc, char** argv)  //  GOOD
{
  ...
}
As to the specific return value, if you don't know what else to return just say return 0;