#include<iostream>
using namespace std;
class Complex
{
public:
    Complex()  { real=0;imag=0; }
    Complex(double r,double i) { real=r; imag=i; }
    Complex operator +(Complex &c2);
    friend ostream& operator<<(ostream&,Complex&);
private:
    double real;
    double imag;
};

Complex Complex::operator+(Complex &c2)
{  return Complex(real+c2.real,imag+c2.imag);  }

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

int main()
{
    Complex c1(2,4),c2(6,10),c3;
    c3=c1+c2;
    cout<<c3;
    return 0;
}
上面这个程序在vc环境中试无法通过的，必须得将第一行修改成为
#include <iostream.h>
同时删去第二行才可以，这是为什么呢