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.

int& foo(int x) {
  int val {++x};
  return val;
}
int boo(int x) {
  return x+10;
}
// suppose these statements comprise function main ...
int& ri { foo(10) };
ri = boo(ri);
std::cout << ri;