(2) 将运算符+和-重载为 complex 类的友元函数。 #include<iostream.h> class complex { public: complex(double r=0.0,double i=0.0) { real=r; imag=i; } //构造函数 friend complex operator + (complex c1,complex c2); //重载运算符+为友元函数 friend complex operator - (complex c1,complex c2); //重载运算符-为友元函数 void display(); //显示复数的值 private: //私有成员 double real; double imag; }; 完成该类的实现并编译运行该程序。

完整实现代码如下：

#include<iostream>
using namespace std;

class complex {
public:
    complex(double r = 0.0, double i = 0.0) {
        real = r;
        imag = i;
    } //构造函数
    friend complex operator+(complex c1, complex c2);  //重载运算符+为友元函数
    friend complex operator-(complex c1, complex c2);  //重载运算符-为友元函数
    void display(); //显示复数的值
private: //私有成员
    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);
}

void complex::display() {
    cout << "(" << real << ", " << imag << "i)" << endl;
}

int main() {
    complex c1(1, 2);
    complex c2(3, 4);
    complex c3 = c1 + c2;
    complex c4 = c1 - c2;
    c1.display();
    c2.display();
    c3.display();
    c4.display();
    return 0;
}

运行结果：

(1, 2i)
(3, 4i)
(4, 6i)
(-2, -2i)

可以看到，重载后的运算符+和- 可以直接对两个复数对象进行运算，且结果正确。