Stream extraction operator in C++

Question

I have the following code:

#include<iostream>
using namespace std;
 int main() 
{
 int x=3;
 cout<<x++<<++x<<x++<<++x<<endl;
return 0; 
}

the output should be 3557 but it is 6747. why???

Also:

#include<iostream>
using namespace std;
 int main() 
{
 int x=3;
    cout <<x++<<endl;
    cout<<++x<< endl;
    cout<<x++<< endl;
    cout<<++x<< endl;
return 0; 
}

The above code gives: 3 5 5 7 (every digit in new line) Can anyone explain why?

There have been many questions on this topic. The first example is undefined behavior. — crashmstr, Mar 25 '14 at 15:37

score 0 · Accepted Answer · edited May 23 '17 at 10:26

0

 int x=3;
 cout<<x++<<++x<<x++<<++x<<endl;

This is undefined behavior, so you could easily get any result.

int x=3;
cout <<x++<<endl; // x = 3, post incremented to 4...
cout<<++x<< endl; // here x = 4 and preincremented to x = 5
cout<<x++<< endl; // x = 5 , postincremented to 6...
cout<<++x<< endl; // so here x = 6 but preincremented to 7

Undefined behavior and sequence points

unexpected output in cout and printf

edited May 23 '17 at 10:26

Community

1
1

answered Mar 25 '14 at 15:41

4pie0

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You should add a link to [this answer](http://stackoverflow.com/a/4176333/2700399) for an explanation of the undefined behavior. – Bart van Nierop Mar 25 '14 at 15:42

Stream extraction operator in C++

1 Answers1