Small Question on statement a = ( b() != c )

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Kani_AVR
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Posted by Kani_AVR: Sun. Oct 2, 2011 - 03:45 PM
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hi all..

I recently came through this like a statement in AVR c project ,and I was wondering whether it is an augmented assignment or a comparison..

a = ( b() != c );
a = ( b != c );

Any help is much appreciated..

thanks.

BR
Kanishka

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AVR Microcontrollers, megaAVR and tinyAVR
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Bronze Markdavid.prentice
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Posted by david.prentice: Sun. Oct 2, 2011 - 03:58 PM
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The compiler will evaluate :
1. b()
2. compare it with c. true or false.
3. assign the result to a.

I have no idea what an "augmented assignment" is.

Note that the order of evaluation could be completely different if you had changed the parentheses.

David.

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sternst
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Posted by sternst: Sun. Oct 2, 2011 - 04:01 PM
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"!=" is an operator like any other with a well defined result (0 if both operands are equal, 1 otherwise). And of course it is also possible to assign this result to a variable.

Stefan Ernst

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Kani_AVR
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Posted by Kani_AVR: Sun. Oct 2, 2011 - 04:37 PM
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Hi Stefan and David..

Thanks a lot for your reply.

BR
Kanishka

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Kani_AVR
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Posted by Kani_AVR: Thu. Oct 6, 2011 - 10:02 PM
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Hi all,

I tried the result to verify this by myself. but the results were not to the expectation..

#include
using namespace std;

int main()
{
	int a,b,c=10;
	a = (b == c);
	cout<<a<<"\n";
	a = (b != c);
	cout<<a<<"\n";	
	
}

the output was 0 1 instead of 1 0 which was expected..
anything wrong here.. ??

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sternst
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Posted by sternst: Thu. Oct 6, 2011 - 10:17 PM
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b has an unspecific random content, so how can you expect something specific?
In your case the random content of b is obviously not 10.

Stefan Ernst

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indianajones11
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Posted by indianajones11: Thu. Oct 6, 2011 - 10:21 PM
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int main() 
{ 
   int a,b,c=10; 
   a = (b == c);

2 of the 3 LOCAL vars. are uninitialized so you can't know what value b will start with. So b == c, tests for equality and is FALSE, etc. from there. You need a good book on C.

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Kani_AVR
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Posted by Kani_AVR: Thu. Oct 6, 2011 - 10:46 PM
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Ohhhhh...

Sorry for the silly question and thanks a lot for your help and time..

BR

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