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

On 21 Sep 2007 05:15:35 GMT, "Guofu Chen" <gchen@[EMAIL PROTECTED]
> wrote:

>Can anyone tell me the different between
>(1)
>int i, j;
>i = j ==1;

This expression invokes undefined behavior.  It is parsed as
	i = (j == 1);
Since j has not been assigned a value, attempting to evaluate it is a
nono.

>cout << i;
>cout << j;

Since this is a C group, you need to define cout and give it a value
before you can ****ft its value.

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

This is parsed as 
	i = (j = 1);
so i is assigned the value of the parenthetical expression which will
be the value assigned to j which is 1.

>cout << i;
>cout << j;
>
>
>Why the result of  (1) is
>
>0 0

Undefined behavior can produce any result.  It could have been  26 and
q.  Most likely, your system initialized j to 0, the == operator
evaluated to false (also 0), and the result of this evaluation was
assigned to i.  At no point do you assign a value to j so it remained
unchanged.

>
>while the result of (2) is
>
>1 1
>
>Thanks! 


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