#include <iostream>

// compile with -Wall to get a warning for this code

int main(int argc, char** argv)
{
    int i = 0;
    int j;

    // undefined behavior.
    // C++ standard says you can not modify the value of a variable 
    // more than once in a statement
    j = ++i + ++i; 

    // this is undefined also because it is not defined whether
    // ++i increments i before or after it adds it self to the second i.
    // "the order in which side effects take place is unspecified"
    j = ++i + i;

    std::cout << j << std::endl;

    return 0;
}