return 0 implicit

Question

The last week on the ACM ICPC Mexico competition, I missed a "return 0" on a C++ program. For this reason we got punished with 20 minutes.

I had read that the standard does not oblige us to write it at the end of a main function. It is implicit, isn't it? How can I prove it?

We were using a Fedora system with a G++ compiler.

Answer 1

You refer to the C++ Standard, chapter 3.6.1 paragraph 5:

A return statement in main has the effect of leaving the main function (destroying any objects with auto- matic storage duration) and calling exit with the return value as the argument. If control reaches the end of main without encountering a return statement, the effect is that of executing return 0;

If you haven't got the Standard at hand, you can show then the paragraph in a Working Draft. Here is one for c++98, which already had this defined.

http://www.kuzbass.ru:8086/docs/isocpp/basic.html#basic.start.main

Answer 2

You could show them the line in Bjarne Stroustrup's book defining the standard where it states it: since it is the canonical standard for the language, it is not open for debate. Unfortunately I don't have a copy to look it up myself.

Answer 3

I once kept getting a wrong answer on an Online Judge because of that too, so I always remembered to add it even before coding the problem.