c++程序，编译器vc++6.0 求大神看看哪错了， 运行结果不对

#include <iostream>

class com
{
public:
    com( int real=0, int image=0 ) : real_(real), image_(image)
    {
    }

private:
    int real_, image_;

    friend std::istream& operator >> ( std::istream&, com& );
    friend std::ostream& operator << ( std::ostream&, const com& );
    friend com operator + ( const com&, const com& );
};

com operator+ ( const com& a, const com& b )
{
    return com( a.real_+b.real_, a.image_+b.image_ );
}

std::ostream& operator << ( std::ostream& output, const com& c )
{
    output << '(' << c.real_ << '+' << c.image_ << "i)";
    return output;
}
std::istream& operator >> ( std::istream& input, com& c )
{
    input >> c.real_ >> c.image_;
    return input;
}

using namespace std;

int main()
{
    com a, b;
    cout << "input a=";
    cin  >> a;
    cout << "input b=";
    cin  >> b;
    cout << "a="   << a << endl;
    cout << "b="   << b << endl;
    cout << "a+b=" << a+b << endl;

    return 0;
}