. 运算符重载为非成员函数-复数加减法

#include<iostream>
using  namespace  std;
class  complex
{
public:
    complex(double  r = 0.0, double  i = 0.0) { real = r; imag = i; }
    friend  complex  operator  +  (complex  c1, complex  c2);        //+重载为成员函数
    friend  complex  operator  -  (complex  c1, complex  c2);          //-重载为成员函数
    void  display();        //输出复数
private:
    double  real;        //复数实部
    double  imag;        //复数虚部
};
//重载函数实现
complex  operator  +(complex  c1, complex  c2)
{

    complex tmp; 
    tmp.real = c1.real + c2.real;
    tmp.imag = c1.imag + c2.imag;
    return tmp;

}
//重载函数实现
complex  operator  -(complex  c1, complex  c2)
{

    complex tmp; 
    tmp.real = c1.real - c2.real;
    tmp.imag = c1.imag - c2.imag;
    return tmp;
}
void  complex::display()
{
    cout << "(" << real << "," << imag << ")" << endl;
}

int  main()
{
    complex  c1(5, 4), c2(2, 10), c3, c4;
    cout << "c1=";  c1.display();
    cout << "c2=";  c2.display();
    c3 = c1 - c2;        //使用重载运算符完成复数减法
    cout << "c3=c1-c2=";
    c3.display();
    c4 = c1 + c2;        //使用重载运算符完成复数加法
    cout << "c4=c1+c2=";
    c4.display();
}