C++输入输出运算符重载（“>>”“<<”）

//输入输出运算符只能用友元函数重载
#include <iostream>
#include <assert.h>
#include <string.h>

using namespace std;

class Complex
{
double re,im;
public:
Complex(double r,double i):re(r),im(i)
{

}
Complex()
{
re = 0;
im = 0;
}
Complex operator!();
Complex operator+(const Complex &obj);
//重载输入输出运算符，只能用友元函数
friend ostream &operator<<(ostream &os,const Complex &c);
friend istream &operator>>(istream &is,Complex &c);
};

Complex Complex::operator +(const Complex &obj)
{
Complex temp;
temp.re = re + obj.re;
temp.im = im + obj.im;
return temp;
}

Complex Complex::operator !()
{
Complex temp;
temp.re = -re;
temp.im = -im;
return temp;
}

ostream & operator<<(ostream &os,const Complex &c)
{
os << c.re;
if(c.im > 0)
os << "+" << c.im << "i" << endl;
else
os << c.im << "i" << endl;
return os;
}

istream & operator>>(istream &is,Complex &c)
{
is >> c.re >> c.im;
return is;
}

int main(int argc,char *argv[])
{
Complex obj1(1,2),obj2(3,4);
Complex obj3 = obj1 + !obj2;
cout << obj3;
cin >> obj3;
cout << obj3;
return 0;
}