Re: Question about namespace

Analysis:
1. tmpval is a mycomplex.
2. mycomplex must be implicitly constuctible from the 0 literal.
3. it could use the first ctor: mycomplex(double).

I assume you declared greater-or-equal like this, just as the error message
says:

class mycomplex
{
   bool operator>=(mycomplex& that);
};

You are not const-correct. Try this instead and the temporary mycomplex(0)
can bind to the now-const reference:

class mycomplex
{
   bool operator>=(const mycomplex& that) const;
};

Notice also, the member function approach above is somewhat incorrect as the
implicit this and that arguments in (this >= that) are subject to differing
conversion rules. Better is:

class mycomplex
{
   friend bool operator>=(const mycomplex& left, const mycomplex& right);
}