实现复数类中的运算符重载2

#include
using namespace std;
class Complex
{
public:
    Complex(){real=0;imag=0;}
    Complex(double r,double i){real=r;imag=i;}
    friend Complex operator+(Complex &c1,Complex &c2);
    friend Complex operator-(Complex &c1,Complex &c2);
    friend Complex operator*(Complex &c1,Complex &c2);
    friend Complex operator/(Complex &c1,Complex &c2);
    Complex operator+(const double &d);//成员函数
    friend Complex operator+(const double &d,Complex &c1);//d+c1只能用友元函数
    void display();
private:
    double real;
    double imag;
};
Complex operator+(Complex &c1,Complex &c2)
{
    return Complex(c1.real+c2.real,c1.imag+c2.imag);
}
Complex operator-(Complex &c1,Complex &c2)
{
    return Complex(c1.real-c2.real,c1.imag-c2.imag);
}
Complex operator*(Complex &c1,Complex &c2)
{
    return Complex(c1.real*c2.real,c1.imag*c2.imag);
}
Complex operator/(Complex &c1,Complex &c2)
{
    return Complex(c1.real/c2.real,c1.imag/c2.imag);
}
Complex Complex::operator+(const double &d)
    {
        return Complex(real+d,imag);
    }
Complex operator+(const double &d,Complex &c1)
    {
        return Complex(d+c1.real,c1.imag);
    }
void Complex::display()
{
    cout<<"("< }
int main()
{
    Complex c1(3,4),c2(5,-10),c3;
    cout<<"c1=";
    c1.display();
    cout<<"c2=";
    c2.display();
    c3=c1+c2;
    cout<<"c1+c2=";
    c3.display();
    c3=c1-c2;
    cout<<"c1-c2=";
    c3.display();
    c3=c1*c2;
    cout<<"c1*c2=";
    c3.display();
    c3=c1/c2;
    cout<<"c1/c2=";
    c3.display();
    c3=c1+2;
    cout<<"c1+2=";
    c3.display();
    c3=2+c1;
    cout<<"2+c1=";
    c3.display();
    return 0;
}