有以下程序，输出结果( )。 #include＜iostream＞ using namespace std class Complex { public: Complex(double r=0,double i=0):re(r),im(i){} double real()const{return re} double imagoconst{return im} Complex operator+(Complex C) const {return Complex(re+c.re,im+c.im)} private: double re,im } int main() { Complex a=Complex(1,1)+Complex(5) cout＜＜a.real()＜＜'+'＜＜a.imag()＜＜'i'＜＜end1 return 0 }