Why c++ program with logical and operator and increment operator gives different output than expected?

Question

I am trying following C code. I my opinion output of this code should be 0 0 0 0. But after executing it output comes as 0 -1 -1 0. Can anybody explain how output comes.

    #include<iostream>
    using namespace std;
    int main()
    {
        int x=-1, y=-1, z=-1;
        int w= ++x && ++y && ++z;
        cout<<x<<" "<<y<<" "<<z<<" "<<w<<endl;
        return 0;
    }

Your title says this is a C question, yet you tag "c++" (and the code uses `cout`). Maybe you should update your question to say C++ or change the tag if you really are looking for a C solution. C and C++ are *very different* languages - don't mix them up or think they are interchangeable. — Jesper Juhl, Aug 15 '18 at 18:25
Thanks for the save, @haccks Instantly regretted kneejerk close. — user4581301, Aug 15 '18 at 18:26

haccks · Accepted Answer · 2018-08-15T18:27:14.603

3

This is because of the short-circuit behaviour of the && operator. ++x evaluated to 0 which will be considered as false. So, only ++x will be evaluated and rest expressions will not be evaluated and final value of the expression ++x && ++y && ++z will be 0 and it will be assigned to w.

edited Aug 15 '18 at 18:27

answered Aug 15 '18 at 18:23

haccks

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This does not explain why `z==0` I would expect `0 -1 -1 -1` – Richard Critten Aug 15 '18 at 18:23
3

@RichardCritten z is -1 w is 0 – Öö Tiib Aug 15 '18 at 18:25
Thanks am blind sorry about that. – Richard Critten Aug 15 '18 at 18:26

Why c++ program with logical and operator and increment operator gives different output than expected?

1 Answers1