increasing var twice in a statement

[Timothy C Prince]

-----Original Message-----
From: Christian Böhme <monodhs@gmx.de>
To: gcc-help@gcc.gnu.org
Date: Fri, 15 Jun 2007 22:09:10 +0200
Subject: Re: increasing var twice in a statement

Chris Wolstenholme wrote:

> 1) The statement was a = ++b + ++b;
> 2) b=3 before this statement
> 3) The operator ++ on the right hand side of the + operator is executed 
> first by rules of precedence. As it is pre-increment, b becomes 4.

.... yielding a (hypothetical) temporary holding the value 4 as the right
hand operand of "+".

> 4)The operator ++ on the left hand side of the + operator is then 
> executed. As it is also pre-increment, b is again altered to become 5.

.... yielding a(nother hypothetical) temporary holding the value 5 as the
left hand operand of "+".

> 5) Then the operator + is executing adding b (now 5) to b (still 5).

.... which would yield 9 (= 5 + 4) according to the above.

> That's only two increments of b, but both before the addition operator.

Try to derive a syntax tree from the expression and evaluate it by
walking that tree using your defined order and you'll arrive at a = 9.

______________________________--
The question was about what result a C standard would dictate, but the C standard in effect says no result can be relied upon in this kind of situation.
Tim Prince