//header

class Foo {
public:
  Foo();
  Foo(const Foo& that);

  Foo& operator=(const Foo& that);

  float x;
};

//source file

Foo::Foo() {
  x= 0;
}

Foo::Foo(const Foo& that) {
  x= that.x;
}

Foo& Foo::operator=(const Foo& that) {
  x= that.x;
  return *this;
}