Question

用c++ 定义一个圆类,计算圆的面积和周长.要求：分别用成员函数和友元函数来求圆的面积和周长.

Answer 1

#include

class Circle

{

public:

Circle():radius(0){}

Circle(double r):radius(r){}

const double area() const

{

return M_PI * radius * radius;

}

const double perimeter() const

{

return 2 * M_PI * radius;

}

friend double area(Circle);

friend double perimeter(Circle);

private:

double radius;

};

double area(Circle c)

{

return M_PI * c.radius * c.radius;

}

double perimeter(Circle c)

{

return 2 * M_PI * c.radius;

}