Why variable always print 0?

Asked Jun 20 '18 at 05:20

Active Jun 20 '18 at 05:20

Viewed 82 times

#include <stdio.h>

int main(void)
{
    int j = 0;
    for(int i = 0; i < 100; i++)
    {
        j = j++;
    }
    printf("%d\n",j);

    return 0;
}

In the above program, I aspect 99 outputs of j variable. but It's always print 0.

I don't understand, Why j always print 0?

asked Jun 20 '18 at 05:20

Jayesh

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Try either `j++` or `j = j + 1`, *not* `j = j++` – Sander De Dycker Jun 20 '18 at 06:49
2

Out of interest, is `j = ++j` now well-defined in C? It is in C++, from C++11. – Bathsheba Jun 20 '18 at 07:00
@SanderDeDycker: Thanks - good to know for those pub quizzes. – Bathsheba Jun 20 '18 at 07:20
@SanderDeDycker no it didn't. – Antti Haapala -- Слава Україні Jun 20 '18 at 07:27
[See the footnote 84](http://port70.net/~nsz/c/c11/n1570.html#note84) – Antti Haapala -- Слава Україні Jun 20 '18 at 07:29
@Bathsheba another good to know for pub quiz ^ – Antti Haapala -- Слава Україні Jun 20 '18 at 07:32
@AnttiHaapala : interesting, so there is a difference in this respect between C11 and C++11. A good write-up : https://stackoverflow.com/questions/22616044/assignment-operator-sequencing-in-c11-expressions/22616368#22616368 . Thanks ! It's good to know. – Sander De Dycker Jun 20 '18 at 07:51
@SanderDeDycker [Jens' answer](https://stackoverflow.com/a/22697426/918959) is the best. There is nothing else needed. – Antti Haapala -- Слава Україні Jun 20 '18 at 07:54
@Bathsheba : my apologies for misleading you ... I missed some important differences – Sander De Dycker Jun 20 '18 at 07:58
@Jayesh The important line in your code, `j = j++`, is just about perfectly meaningless. If you want to add 1 to `j`, you can use `j = j + 1` or `j++`. But never try to mash the two together as `j = j++`, because the results are undefined. – Steve Summit Jun 20 '18 at 10:09

Why variable always print 0?

0 Answers0