prob-04-main.cpp:21:3: error: unknown type name 'c'
  c -= d;
  ^
prob-04-main.cpp:21:5: error: expected unqualified-id
  c -= d;
    ^
prob-04-main.cpp:22:3: error: C++ requires a type specifier for all declarations
  discriminant = Discriminant(a, b, c);
  ^
prob-04-main.cpp:22:31: error: use of undeclared identifier 'a'
  discriminant = Discriminant(a, b, c);
                              ^
prob-04-main.cpp:22:34: error: use of undeclared identifier 'b'
  discriminant = Discriminant(a, b, c);
                                 ^
prob-04-main.cpp:22:37: error: use of undeclared identifier 'c'
  discriminant = Discriminant(a, b, c);
                                    ^
prob-04-main.cpp:24:3: error: expected unqualified-id
  if (discriminant < 0) {
  ^
prob-04-main.cpp:27:3: error: expected unqualified-id
  else if (discriminant == 0) {
  ^
prob-04-main.cpp:31:3: error: expected unqualified-id
  else {
  ^
prob-04-main.cpp:61:9: error: use of undeclared identifier 'root_one'
        root_one = root_two = -b / (2 * a);
        ^
prob-04-main.cpp:61:20: error: use of undeclared identifier 'root_two'
        root_one = root_two = -b / (2 * a);
                   ^
11 errors generated.