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C Problem?

unsigned char x=1;
x=(x++)<<3;

Using uVision 6.12
Gives answer of 8
It shifts binary 1 left and doesn't increment.
(even when optimization set to level 0)

Using Micorsoft C++ 6.0
Gives answer of 9
It shifts binary 1 left then increments.

I was a little confused with both answers because I was thought that
the increment would happen first because of the ( ) around x++ then
shift left three giving 16 but that's not the case.

This gives me 16 in both Keil and MS.

x=(++x)<<3; works it gives 16

Parents

0 Mark Odell over 24 years ago in reply to Andrew Neil
Since this equation produces undefined behavior, there is no right answer IMHO. See:

http://www.eskimo.com/~scs/C-faq/q3.3.html

I suggest:

x = x + 1 << 3;
and remember that + happens before <<.

:-)

- Mark
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0 Mark Odell over 24 years ago in reply to Andrew Neil
Since this equation produces undefined behavior, there is no right answer IMHO. See:

http://www.eskimo.com/~scs/C-faq/q3.3.html

I suggest:

x = x + 1 << 3;
and remember that + happens before <<.

:-)

- Mark
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0 Jon Young over 24 years ago in reply to Mark Odell
To Keil Discussion Forum site:

Add the following suggestion to your "Tips for Posting Measages".

If you type an URL like
<pre>TheUrl</pre>

then add a space before the </pre>.

If you don't, one can not follow the hyperlink (using IE5.5) by clicking on it.
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0 Andrew Neil over 24 years ago in reply to Jon Young

Actually, there is no need to use the &ltpre&gt and &lt/pre&gt tags for URLs at all - the forum automatically makes URLs clickable (as it says in the Tips).

It seems that it's this automatic conversion to a link which has gone wrong - it's caught the closing &lt/pre&gt tag inside the closing &lt/a&gt link tag!
So yes, a space (or newline?) before the &lt/pre&gt would probably have fixed it.
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0 Mark Odell over 24 years ago in reply to Jon Young

Sorry about that, I didn't mean to use the pre tag at all.

- Mark
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