# c and php operations

- Thread: https://externals.io/message/54252
- Original archive: https://news-web.php.net/php.internals/54252
- Started by Adir Kuhn on 2011-07-29T17:20:17+00:00
- Messages: 2
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## #54252 — Adir Kuhn — 2011-07-29T17:20:17+00:00

URL: https://externals.io/message/54252#54252

Hello guys,

while I'm studing some c codes i found this page:
http://www.nicksays.co.uk/2009/05/awesome-c-exam-question/

and this code:

#include <stdio.h>
 int func (int a, int b) {
	static int c = 1;
	return a + b * (c *= -1);}
 int main () {
	int a = 2, b = 3;
	int c = func(a, b);

	a *= a++;
	b *= ++b;

	printf("%d %d %d %d\n", a, b, c, func(a, b));}

thats prints: 5 16 -1 21

then I made a similar php script:

<?php
function func ($a, $b) {
    static $c =1;
    return $a + $b * ($c *= -1);
 }

function main() {
    $a = 2;
    $b = 3;
    $c = func($a, $b);

    $a *= $a++;
    $b *= ++$b;

    printf("%d %d %d %d\n", $a, $b, $c, func($a, $b));
}
main();
?>

and for my surprise its prints: 6 16 -1 22

so, somebody know and can explain me wtf happened?

Thanks!

Adir Kuhn

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## #54253 — Joey Smith — 2011-07-29T18:01:32+00:00

URL: https://externals.io/message/54252#54253 · In reply to: #54252

> Hello guys,
> 
> while I'm studing some c codes i found this page:
> http://www.nicksays.co.uk/2009/05/awesome-c-exam-question/
> 
> and this code:
> 
> #include <stdio.h>
>  int func (int a, int b) {
> 	static int c = 1;
> 	return a + b * (c *= -1);}
>  int main () {
> 	int a = 2, b = 3;
> 	int c = func(a, b);
> 
> 	a *= a++;
> 	b *= ++b;


I'm no expert in C, but my understanding is that the two expressions immediately
above are UNDEFINED because there is only one sequence point, but the objects are
modified twice (*= and ++). See http://c-faq.com/expr/seqpoints.html

gcc appears to agree with me via the -Wsequence-point flag:

joey@banshee:0$cat > a.c
#include <stdio.h>

int func (int a, int b) {
        static int c = 1;
        return a + b * (c *= -1);
}

int main () {
        int a = 2, b = 3;
        int c = func(a, b);

        a *= a++;
        b *= ++b;

        printf("%d %d %d %d\n", a, b, c, func(a, b));
}
joey@banshee:0$gcc -Wsequence-point a.c
a.c: In function ‘main’:
a.c:12:4: warning: operation on ‘a’ may be undefined
a.c:13:4: warning: operation on ‘b’ may be undefined


If my interpretation is correct, I'm not sure how much time we need to spend
around the question.