#include <iostream>
#include <cmath>
using namespace std;
class Complex
{
    public:
        Complex();
        Complex(double r);
        Complex(double r,double i);
        void display();
        friend Complex operator+(Complex &c1,Complex &c2);
    private:
        double real;
        double imag;
};

Complex::Complex()
{
    real=0;
    imag=0;
}

Complex::Complex(double r)
{
    real=r;
    imag=0;
}

Complex::Complex(double r,double i)
{
    real=r;
    imag=i;
}

Complex operator+(Complex &c1,Complex &c2)
{
    return Complex(c1.real+c2.real,c1.imag+c2.imag);
}

void Complex::display()
{
    if(imag>0)
        cout<<"("<<real<<"+"<<imag<<"i)"<<endl;
    else if(imag==0)
        cout<<"("<<real<<")"<<endl;
    else
        cout<<"("<<real<<"-"<<fabs(imag)<<"i)"<<endl;
}

int main()
{
    Complex c1(2,1),c;
    c=c1+2.5;     // 把这行注释掉能编译通过，编译器报错说我的重载+函数有问题。但是我没找出来。还请各位指教。               
    cout<<"c1+2.5=";
    c.display();
    return 0;
}

恩 好的 谢谢。这个const不应该是加不加都可以吗？

好的谢谢