What will be printed out as a result of the progra

What will be printed out as a result of the program execution?

#include <iostream>

void func(int a, int b, int c, int d)
{
   std::cout << a << b << c << d;
}

int main()
{
   int a = 0;
   func(++a, a++, ++a, a++);
   return 0;
}

1234
0123
4220
4240
Undefined behavior
Compilation error

Explanation

The order of calculating the arguments passed into the function is not defined. That's why the result of this code execution is undefined behavior. You may read the details here: Sequence point.