有以下程序: #include <iostream> using namespace std; class Complex { public: Complex(double r=0,double i=0):re(r),im(i){ double zeal() const {return re;} double imag() const {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'<<end 1; return 0; }程序执行后的输出结果是______。