class Complex{public:    explicit Complex(double real, double imaginary = 0)    : real_(real), imaginary_(imaginary)    {    }    Complex& operaor+=(const Complex& o)    {         real_ += o._real_;         imaginary_ += o.imaginary_;         return *this;    }    Complex& operator++()    {         ++real_;         return *this;    }    const Complex operator++(int)// to avoid this expression: a++++    {     Complex tmp(*this);         ++*this;         return tmp;    }    ostream& Print(ostream& os) const    {        return os << ....;    }private:    double real_, imaginary_;};const Complex operator+(const Complex& a, const Complex& b){    Complex ret(a);    ret += b;    return ret;}ostream& operator<<(ostream& os, const Complex& c){    return c.Print(os);}