/in/foo.c: In function 'main':
/in/foo.c:34:9: error: 'cin' undeclared (first use in this function)
  while (cin >> a >> b >> c && !(a == -1 && b == -1 && c == -1)) {
         ^~~
/in/foo.c:34:9: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:35:3: error: 'cout' undeclared (first use in this function)
   cout << "w(" << a << ", " << b << ", " << c << ") = " << find(a, b, c) << endl;
   ^~~~
/in/foo.c:35:77: error: 'endl' undeclared (first use in this function)
   cout << "w(" << a << ", " << b << ", " << c << ") = " << find(a, b, c) << endl;
                                                                             ^~~~