#ifndef _COMPLEX_H_ #define _COMPLEX_H_ #include namespace complex { class Complex { public: // Should += return a reference? // (Answer: ?) Complex &operator+=(const Complex &a) { this->real_ += a.real_; this->imag_ += a.imag_; return *this; } private: double real_, imag_; }; // class Complex } // namespace complex #endif // _COMPLEX_H_