Re: A question about '=='' in C++!

"Guofu Chen" <gchen@[EMAIL PROTECTED]
> wrote in news:clcm-20070921-0029
@[EMAIL PROTECTED]
> Can anyone tell me the different between
> (1)
> int i, j;
> i = j ==1;
> cout << i;
> cout << j;

The equality (==) operator has a higher associativity than the assignment 
(=) operators, so the second line is:

i = (j == 1);

if we add the implicit parentheses.  What is happening is that you are 
assigning the result of the j == 1 operation to i.

j is undefined at this point, but almost certainly not equal to 1 so the 
result of j == 1 is going to be false, which will become 0 when implicitly

cast to an int by the assignment operator.

So i becomes 0 and j is left undefined (some implementations initialize 
variables to 0, some don't).

> and
> (2)
> int i, j;
> i = j = 1;
> cout << i;
> cout << j;

i = j = 1;
Assignment is right associative, so the right side of each assignment 
operator is evaluated before the left, giving us (with implicit
parentheses 
added):

i = (j = 1);

So j becomes 1 then i becomes the value of j (which is 1).

HTH.

--
Anabelle.
-- 
comp.lang.c.moderated - moderation address: clcm@[EMAIL PROTECTED]
 -- you must
have an appropriate newsgroups line in your header for your mail to be
seen,
or the newsgroup name in square brackets in the subject line.  Sorry.