c++官方文档-class

#include <iostream>
using namespace std;class Circle
{
double radius;
public:
Circle(double r)
{
radius = r;
}
double area()
{
return * radius;
}
};
class Cylinder
{
Circle base;
double height;
public:
Cylinder(double r, double h)
: base(r), height(h)
{
}
double volume()
{
return base.area() * height;
}
};
//uniform initializer
//Cylinder::Cylinder(double r, double h)
// : base { r }, height { h }
//{
//}
class Rectangle
{
int width, height;
public:
Rectangle();
Rectangle(int, int);
void set_values(int, int);
int area(void)
{
return width * height;
}
;
};
Rectangle::Rectangle()
{
width = ;
height = ;
}
Rectangle::Rectangle(int x, int y)
: width(x), height(y)
{
}//Rectangle::Rectangle(int a, int b)
//{
// width = a;
// height = b;
//}
void Rectangle::set_values(int x, int y)
{
width = x;
height = y;
}int main()
{
Rectangle rect(, );
int myarea = rect.area();
cout << myarea << endl;
// Circle foo(10.0); // functional form
Circle bar = 20.0; // assignment init.
Circle baz { 30.0 }; // uniform init.
Circle qux = { 40.0 }; // POD-like
// cout << foo.area() << endl;
cout << bar.area() << endl;
cout << baz.area() << endl;
cout << qux.area() << endl;
Rectangle rectb; // default constructor called
Rectangle rectc(); // function declaration (default constructor NOT called)
Rectangle rectd { }; // default constructor called Cylinder foo(, );
cout << "foo's volume: " << foo.volume() << '\n';
Rectangle* foop;
foop = &rect;
cout << foop->area() << endl;
delete foop;
return ;
}