请各位看看这个C++程序哪儿错了啊。谢谢啊。

#include <iostream>
using namespace std;
class Complex
{public:
Complex(){real=0;imag=0;}
Complex(double r,double i){real=r;imag=i;}
double get_real();
double get_imag();
void display();
friend ostream& operator <<(ostream&,Complex&);
private:
double real;
double imag;
};

double Complex::get_real()
{return real;}

double Complex::get_imag()
{return imag;}

ostream& operator<< (ostream& output,Complex &c)
{
output<<"("<<c.real;
if(c.imag>0)
output<<"+"<<c.imag<<"i"<<")";
else
output<<c.imag<<"i"<<")";
return output;
}

Complex operator + (Complex &c1,Complex &c2)//因为是公有函数，所以可以调用
{
return Complex(c1.get_real()+c2.get_real(),c1.get_imag()+c2.get_imag());
}

#include <iostream.h>
class Complex
{public:
Complex(){real=0;imag=0;}
Complex(double r,double i){real=r;imag=i;}
double get_real();
double get_imag();
void display();
friend ostream& operator <<(ostream&,Complex&);
private:
double real;
double imag;
};

double Complex::get_real()
{return real;}

double Complex::get_imag()
{return imag;}

ostream& operator<< (ostream& output,Complex &c)
{
output<<"("<<c.real;
if(c.imag>0)
output<<"+"<<c.imag<<"i"<<")";
else
output<<c.imag<<"i"<<")";
return output;
}

Complex operator + (Complex &c1,Complex &c2)//因为是公有函数，所以可以调用
{
return Complex(c1.get_real()+c2.get_real(),c1.get_imag()+c2.get_imag());
}

int main() <

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