class RationalNumber {
    int fenzi,fenmu;
public:
    RationalNumber(int zi,int mu);
    void print();
/***********************************************/
//错误出在这儿
    friend RationalNumber&
        operator+ (RationalNumber& left,RationalNumber& right);
    friend RationalNumber&
        operator- (RationalNumber& left,RationalNumber& right);
    friend RationalNumber&
        operator* (RationalNumber& left,RationalNumber& right);
    friend RationalNumber&
        operator/ (RationalNumber& left,RationalNumber& right);
/***************************************/
};

帮帮忙啊