Write if the following code fragment doesn't compile or write  if the code compiles but has undefined behavior when executed. Otherwise, write the exact text written to the standard output stream.

void secret(int& x, int& y) {
  x = x - y;
  y = y + x;
  x = y - x;
}
// assume the following statements comprise function main ...
int one{4}, two{3};
secret(one, two);
int x1{one}, x2{two};
secret(two, two);
int x3{two};
secret(one, one);
int x4{one};
std::cout << x1 << ',' << x2 << ',' << x3 << ',' << x4;