Weird result for modulus operation

[Ang Way Chuang]

Andrew Pinski wrote:
> On Tue, Apr 29, 2008 at 9:08 PM, Ang Way Chuang <wcang@nav6.org> wrote:
>>  Thanks for the speedy reply. But why this code:
>>
>>         int a = 17, b = 16;
>>         a = a++ % 16;
>>
>>  results in a = 2 then? I think I need to know what is sequence point. I'll
>> google that.
> 
> As I mentioned, the code is undefined so it could be any value.

Is there any flag in gcc that can provide warning to code that relies on 
undefined behaviours?

> 
> Thanks,
> Andrew Pinski
>