C++操作符重载的注意事项

关于C++操作符重载，可以用类内的成员运算符重载或友元函数。但是注意两个不能同时出现，不然编译出错。

#include<iostream>
using namespace std;
class Complex{
    
    
  public:
    Complex(int r=0,int i=0)
     {
    
    
      real = r;
      imag = i;
     }
   //#if 0
     Complex operator+(Complex &c) {
    
    
         cout << " internal function is called" << endl;
         Complex c2;
         c2.real = this->real + c.real;
         c2.imag = this->imag + c.imag;
         return c2;
     }
//    #endif 
     void print();
     friend Complex operator+(int a,Complex &c2); //声明友元运算符重载函数,+的左侧是整数,右侧是类的对象 
     friend Complex operator+(Complex c1,int a);//声明友元运算符重载函数,+的右侧是整数,左侧是类的对象
//     friend Complex operator+(Complex c1,Complex c2);//声明友元运算符重载函数,+的右侧是整数,左侧是类的对象 
  private:
    int real;
    int imag;
};
Complex operator+(int a,Complex &c2)  //定义友元运算符重载函数,+的左侧是整数,右侧是类的对象 
{
    
    
  Complex temp;
  cout << "friend function 1 is called" << endl;
  temp.real = a+c2.real;
  temp.imag = c2.imag;
  return temp;
}
Complex operator+(Complex c1,int a)//定义友元运算符重载函数,+的右侧是整数,左侧是类的对象 
{
    
    
  Complex temp;
  cout << "friend function 2 is called" << endl;
  temp.real = c1.real+a;
  temp.imag = c1.imag;
  return temp;
} 
#if 0
Complex operator+(Complex c1,Complex c2)
{
    
    
  Complex temp;
  cout << "friend function 3 is called" << endl;
  temp.real = c1.real+c2.real;
  temp.imag = c1.imag+c2.imag;
  return temp;
}
#endif

void Complex::print()
{
    
    
 cout<<real<<"+"<<imag<<'i'<<endl;
}

int main()
{
    
    
 Complex co1(30,40),co2(30,40),co3,co4;
 co1.print();
 
 co3=100+co1;  //co3=operator+(100,co1); 
 co3.print();
 
 co3=co2+100;  //co3=operator+(co2,100);
 co3.print();
 
 co4=co2+co3;
 co4.print();
 
 return 0;
}