What is the difference betweeen something like this
friend Circle copy(const Circle &);
and something like this
friend
friend Circle copy(const Circle &);
The value of parameter will not be changed during the function calls.
friend Circle copy(const Circle &)const ;
The function is an accessor that does not change any value of class members. Generally, there are to types of functions: accessors and mutators. Accessor: examines but does not change the state of its object.