The best match for an operator

When I am compiling the following program

#include "stdafx.h"

#include <iostream>

#include <complex>

class Complex_

{

public:

    double real, image;

    Complex_(): real( 0 ), image( 0 ) {}

    Complex_( double theReal, double theImage = 0.0 ):

    real( theReal ), image( theImage ) {}

    Complex_ & operator+=( const Complex_ & rhs )

    {

        real += rhs.real;

        image += rhs.image;

        return *this;

    }

    const Complex_ operator+( double d )

    {

        return Complex_( real + d );

    }

    operator double() const

    {

        return real;

    }

};

const Complex_ operator+(const Complex_& lhs, const Complex_& rhs)

{

    return Complex_( lhs )+= rhs;

}

int _tmain(int argc, _TCHAR* argv[])

{

    Complex_ c1( 10, 15 ), c2( 12, 14 );

    Complex_ c3;

    c3 = c1.operator+( c2 );

    std::cout << "c1.real = " << c1.real << ", c1.image = " << c1.image <<
std::endl;

    std::cout << "c2.real = " << c2.real << ", c2.image = " << c2.image <<
std::endl;

    std::cout << "c3.real = " << c3.real << ", c3.image = " << c3.image <<
std::endl;

    c3 = c1 + c2;

    std::cout << "c1.real = " << c1.real << ", c1.image = " << c1.image <<
std::endl;

    std::cout << "c2.real = " << c2.real << ", c2.image = " << c2.image <<
std::endl;

    std::cout << "c3.real = " << c3.real << ", c3.image = " << c3.image <<
std::endl;

    return 0;

}

I have gotten the errors

complex.cpp(51) : error C2666: 'Complex_::operator +' : 3 overloads have
similar conversions

complex.cpp(23): could be 'const Complex_ Complex_::operator +(double)'

complex.cpp(35): or 'const Complex_ operator +(const Complex_ &,const
Complex_ &)'

or 'built-in C++ operator+(double, double)'

while trying to match the argument list '(Complex_, Complex_)'

note: qualification adjustment (const/volatile) may be causing the ambiguity

Is not the operator 'const Complex_ operator +(const Complex_ &,const
Complex_ &)' best match for the statement c3 = c1 + c2;, is it?

Vladimir Grigoriev