（3）定义一个定义完整的类（是可以当作独立的产品发布，成为众多项目中的“基础工程”）。这样的类在(2)的基础上，，扩展+、-、*、/运算符的功能，使之能与double型数据进行运算。设Complex c; double d; c+d和d+c的结果为“将d视为实部为d的复数同c相加”，其他-、*、/运算符类似。
class Complex {public:Complex(){real=0;imag=0;}Complex(double r,double i){real=r; imag=i;}Complex operator+(const Complex &c2);Complex operator-(const Complex &c2);Complex operator*(const Complex &c2);Complex operator/(const Complex &c2);void display();private:double real;double imag;};//下面定义成员函数//下面定义用于测试的main()函数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();return 0;}
#include <iostream>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+(double d1, Complex &c2); friend Complex operator+(Complex &c1, double d2); friend Complex operator-(Complex &c1, Complex &c2); friend Complex operator-(double d1, Complex &c2); friend Complex operator-(Complex &c1, double d2); friend Complex operator*(Complex &c1, Complex &c2); friend Complex operator*(double d1, Complex &c2); friend Complex operator*(Complex &c1, double d2); friend Complex operator/(Complex &c1, Complex &c2); friend Complex operator/(double d1, Complex &c2); friend Complex operator/(Complex &c1, double d2); void display();private: double real; double imag;};Complex operator+(Complex &c1, Complex &c2){ Complex c; c.real=c1.real+c2.real; c.imag=c1.imag+c2.imag; return c;}Complex operator+(double d1, Complex &c2){ Complex c(d1,0); return c+c2;}Complex operator+(Complex &c1, double d2){ Complex c(d2,0); return c1+c;}Complex operator-(Complex &c1, Complex &c2){ Complex c; c.real=c1.real-c2.real; c.imag=c1.imag-c2.imag; return c;}Complex operator-(double d1, Complex &c2){ Complex c(d1,0); return c-c2;}Complex operator-(Complex &c1, double d2){ Complex c(d2,0); return c1-c;}Complex operator*(Complex &c1, Complex &c2){ Complex c; c.real=c1.real*c2.real-c1.imag*c2.imag; c.imag=c1.imag*c2.real+c1.real*c2.imag; return c;}Complex operator*(double d1, Complex &c2){ Complex c(d1,0); return c*c2;}Complex operator*(Complex &c1, double d2){ Complex c(d2,0); return c1*c;}Complex operator/(Complex &c1, Complex &c2){ Complex c; c.real=(c1.real*c2.real+c1.imag*c2.imag)/(c2.real*c2.real+c2.imag*c2.imag); c.imag=(c1.imag*c2.real-c1.real*c2.imag)/(c2.real*c2.real+c2.imag*c2.imag); return c;}Complex operator/(double d1, Complex &c2){ Complex c(d1,0); return c/c2;}Complex operator/(Complex &c1, double d2){ Complex c(d2,0); return c1/c;}void Complex::display(){ cout<<"("<<real<<","<<imag<<"i)"<<endl;}int main(){ Complex c1(3,4),c2(5,-10),c3; double d=11; cout<<"c1="; c1.display(); cout<<"c2="; c2.display(); cout<<"d="<<d<<endl<<endl; cout<<"下面是重载运算符的计算结果: "<<endl; c3=c1+c2; cout<<"c1+c2="; c3.display(); cout<<"c1+d="; (c1+d).display(); cout<<"d+c1="; (d+c1).display(); c3=c1-c2; cout<<"c1-c2="; c3.display(); cout<<"c1-d="; (c1-d).display(); cout<<"d-c1="; (d-c1).display(); c3=c1*c2; cout<<"c1*c2="; c3.display(); cout<<"c1*d="; (c1*d).display(); cout<<"d*c1="; (d*c1).display(); c3=c1/c2; cout<<"c1/c2="; c3.display(); cout<<"c1/d="; (c1/d).display(); cout<<"d/c1="; (d/c1).display(); return 0;}
一旦有了意志，脚步也会轻松起来。
