arithmetic operation differs if variable is char or int

Question

I have the following code

#include <stdio.h>

int main() {
    char y=3, res=0;
    res = ( (++y) * (++y) );
    printf("res=%d    y=%d \n", res, y);
    return 0;
}

The result is:

res=20    y=5

Now when i change variable to int it gives different results

#include <stdio.h>

int main() {
    int y=3, res=0;
    res = ( (++y) * (++y) );
    printf("res=%d    y=%d \n", res, y);
    return 0;
}

The result is:

res=25    y=5

What happened to make res value change?

http://stackoverflow.com/q/949433/168175, haven't earned a dupe hammer for C so will leave to someone else — Flexo, Jul 02 '16 at 13:09
Did you really put any effort in searching about the solution ? — Itban Saeed, Jul 02 '16 at 13:13
@2501 i tried to search but it wasn't clear to me what should i search for — Nasr, Jul 02 '16 at 13:13
"_Please use search next time before asking_" -- Good advice, but frankly, searching "char++ vs int++" will not give any answer. — Spikatrix, Jul 02 '16 at 13:22

score 1 · Answer 1 · answered Jul 02 '16 at 13:10

1

What you're doing there is undefined behavior. If it were defined (either by the spec or by the implemetation), you'd get the same result no matter what data type you used. The value will also change due to optimization.

answered Jul 02 '16 at 13:10

Paul Stelian

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arithmetic operation differs if variable is char or int

1 Answers1