c++ Very important

Question

int z = 10;
cout << ++z << z << z++ << z<<"\n";
why?result different.

Answer 1

The order in which your z++ and ++z statements are evaluated is undefined, so is the effect of your code.
Discussion : [https://stackoverflow.com/questions/33445796/increment-and-decrement-with-cout-in-c]

Avoid doing the incremental/decremental operation "in a row" inside the cout. That causes undefined behavior.

Example: Compare two groups together. They both do the same operation but as you clearly see, former expresion's behavior is completely undefiend.

#include <iostream>
using namespace std;

int main()
{
int x = 1;
int y = 2;

cout << x++ << " " << ++x << " " << --y << " " << y++ << "\n\n";

x = 1;
y = 2;

cout << x++ << endl;
cout << ++x << endl;
cout << --y << endl;
cout << y++ << endl;
}

Output:

2 3 2 2

1
3
1
1

Live link : [http://cpp.sh/8xuaw]

Answer 2

Just adding another related thread to the question:

https://stackoverflow.com/questions/4176328/undefined-behavior-and-sequence-points