友元函数咋利用静态成员和返回

Question

class Circle

{

private:

double radius;

public:

static double PI;

Circle(double a=0);

Circle(Circle &c);

~Circle();

1
void setRadius(double a);

double  getRadius();
double  circumference();
double  area();
friend double  fCircle_L(Circle &r);
friend double  fCircle_S(Circle &r);

};
double Circle::PI=3.1415;
Circle::Circle(double a):radius(a)
{
cout<<"Constructor run"<<endl;
}
Circle::Circle(Circle &c){
radius=c.radius;
cout<<"CopyConstructor run"<<endl;
}
Circle::~Circle()
{
cout<<"Destructor run"<<endl;
}
void Circle::setRadius(double a)
{
radius=a;
}
double Circle::getRadius(){
return radius;
}
double Circle::circumference(){
return (2PIradius);
}
double Circle::area()
{
return (PIradiusradius);
}
double fCircle_L(Circle &r)
{
r=r.radius;
}
double fCircle_S(Circle &r)
{
r=r.radius;
}好兄弟，最后该咋返回呢

Answer 1

double fCircle_L(Circle &r)
{
r=r.radius;
}
double fCircle_S(Circle &r)
{
r=r.radius;
}
返回什麽要看你定义着两个函数的意义啊。都不清楚意义，怎么说返回啥呢
你着两个函数要实现什麽功能呢