以下是博主在学习完运算符重载和友元函数后编写的一个例子，实现一个复数的基本运算。
定义的头文件：
/******************************************************************
complex.h Defination of the complex
******************************************************************/
#ifndef _complex_
#define _complex_
#include<cmath>
#include<iostream>
using std::sqrt ;
using std::ostream; // Error : ‘ostream’ does not name a type
using std::istream;
class Complex{
private:
double real ;
double imag ;
public:
Complex( double real=0 , double imag=0 ) { this->real = real ; this->imag = imag ; }
void zero() { real = imag = 0 ; }
double module() { return sqrt(real*real+imag*imag); }
double angle() { return atan2(imag,real); }
// operator overloading
/******************************************************/
Complex operator+(const Complex & com) const;
Complex operator-(const Complex & com) const;
Complex operator*(const Complex & com) const ;
Complex operator/(const Complex & com) const;
Complex operator~() const;
/*******************************************************/
/******************************************************************/
// template overloading for the general operation of built-in type
Complex operator+(double value);
Complex operator-(double value);
Complex operator*(double value);
Complex operator/(double value);
// friend functions
friend ostream & operator<<( ostream & os , Complex & com );
friend Complex operator+( double value , Complex & com );
friend istream & operator>>( istream & is , Complex & com );
friend Complex operator+( double value , Complex & com );
friend Complex operator-( double value , Complex & com );
friend Complex operator*( double value , Complex & com );
friend Complex operator/( double value , Complex & com );
};
#endif实现的文件：
/***********************************************
Realization of the Complex
************************************************/
#include "complex.h"
#include <iostream>
using std::ostream;
using std::istream;
/*
Complex( double real=0 , double imag=0 ) { this->real = real ; this->imag = imag ; }
void zero() { real = imag = 0 ; }
double module() { return sqrt(real*real+imag*imag); }
double angle() { return atan2(imag,real); }
// Operator overloading
Complex operator+(const Complex & com) const;
Complex operator-(const Complex & com) const;
Complex operator*(const Complex & com) const ;
Complex operator/(const Complex & com) const;
Complex operator~() const;
// Template overloading for the general operation of built-in type
Complex operator+(double value);
Complex operator-(double value);
Complex operator*(double value);
Complex operator/(double value);
// Friend functions
friend ostream & operator<<( ostream & os , Complex & com );
friend Complex operator+( double value , Complex & com );
friend istream & operator>>( istream & is , Complex & com );
friend Complex operator+( double value , Complex & com );
friend Complex operator-( double value , Complex & com );
friend Complex operator*( double value , Complex & com );
friend Complex operator/( double value , Complex & com );
*/
/***********************************************************
Operator Overloading
***********************************************************/
Complex Complex::operator+(const Complex & com) const{
Complex result ;
result.real = this->real + com.real ;
result.imag = this->imag + com.imag ;
return result ;
}
Complex Complex::operator-(const Complex & com) const{
Complex result ;
result.real = this->real - com.real ;
result.imag = this->imag - com.imag ;
return result ;
}
Complex Complex::operator*(const Complex & com) const{
Complex result ;
result.real = (this->real) * com.real - (this->imag*com.imag);
result.imag = this->real*com.imag + this->imag*com.real ;
return result ;
}
Complex Complex::operator/(const Complex & com) const{
Complex result ;
result.real = (this->real*com.real + this->imag*com.imag)/(com.real*com.real+com.imag*com.imag);
result.real = (this->imag*com.real - this->real*com.imag)/(com.real*com.real+com.imag*com.imag);
return result ;
}
Complex Complex::operator~()const{
Complex result ;
result.real = (this->real) ;
result.imag = -this->imag ;
return result ;
}
/*******************************************************************************
Template overloading for the general operation of built-in type
********************************************************************************/
Complex Complex::operator+(double value){
Complex result ;
result.real = this->real+value;
result.imag = this->imag;
return result ;
}
Complex Complex::operator-(double value){
Complex result ;
result.real = this->real-value;
result.imag = this->imag;
return result ;
}
Complex Complex::operator*(double value){
Complex result ;
result.real = this->real*value;
result.imag = this->imag*value;
return result ;
}
Complex Complex::operator/(double value){
Complex result ;
result.real = this->real/value;
result.imag = this->imag/value;
return result ;
}
/**********************************************************
friend functions
***********************************************************/
ostream & operator<<( ostream & os , Complex & com ){
os<<com.real<<'+'<<com.imag<<'j';
return os ;
}
istream & operator>>( istream & is , Complex & com ){
std::cout<<"Enter the real part :";
is>>com.real;
is.clear();
std::cout<<"Enter the image part:";
is>>com.imag;
return is ;
}
// Behold this part , Never get the Istream wrong again !!!!!
Complex operator+( double value , Complex & com ){
Complex result ;
result.real = com.real+value;
result.imag = com.imag;
return result ;
}
Complex operator-( double value , Complex & com ){
Complex result ;
result.real = com.real-value;
result.imag = com.imag;
return result ;
}
Complex operator*( double value , Complex & com ){
Complex result ;
result.real = com.real*value;
result.imag = com.imag*value;
return result ;
}
Complex operator/( double value , Complex & com ){
Complex result ;
result.real = com.real/value;
result.imag = com.imag/value;
return result ;
}测试文件：
#include "complex.h"
#include<iostream>
using namespace std ;
int main(){
Complex a(3.0,4.0);
Complex c ;
Complex result ;
while( std::cin>>c )
{
std::cout<<" c is "<<c<<'\n';
std::cout<<" complex conjugate is "<<(result=~c)<<'\n';
std::cout<<" a is "<<a<<'\n';
std::cout<<" a + c is "<<(result=a+c)<<'\n';
std::cout<<" a - c is "<<(result=a-c)<<'\n';
std::cout<<" a * c is "<<(result=a*c)<<'\n';
std::cout<<" a / c is "<<(result=a/c)<<'\n';
std::cout<<" the mod of c is "<<c.module()<<'\n';
std::cout<<" the angle of c is "<<c.angle()<<'\n';
}
return 0 ;
}在编写时，博主遇到了一个问题：
invalid initialization of non-const reference of type ‘Complex&’ from an rvalue of type ‘Complex’
这是由于函数的返回是一个暂时的量所导致的，所以需要将结果用一个变量保存起来，否则就会报错。
因此就有了以上的写法：(result=a/c)
关于这个问题可以参考：https://blog.csdn.net/u011068702/article/details/64443949