cpp-work/test1/20200311-2.cpp

#include "iostream"

using namespace std;

class Circle {
public:
    Circle(int r);
    Circle();

    const double PI = 3.1415926;

    double getLength();

    double getArea();

    double getRadius();
private:

    double radius = 0;
};

double Circle::getLength() {
    return radius * 2 * PI;
}

double Circle::getArea() {
    return radius * radius * PI;
}

double Circle::getRadius() {
    return radius;
}

Circle::Circle(int r) : radius(r) {}
Circle::Circle() : radius(0) {}

int main() {
    Circle circle(17);
    cout << "Area | Length | Radius" << endl;
    cout << circle.getArea() << endl << circle.getLength() << endl << circle.getRadius();
}

// --------------------------------------------------------------

class Circle2 {
public:
    const double PI = 3.1415926;
    void printArea();
    void printLength();
    void printRadius();

    Circle2(double radius) : radius(radius) {
        area = radius * radius * PI;
        length = radius * 2 * PI;
    }

    Circle2(const Circle2 &c2) {
        radius = c2.radius;
        length = c2.length;
        area = c2.area;
    }

private:
    double radius = 0;
    double length = 0;
    double area = 0;
};

void Circle2::printArea() {
    cout << "Area: " << area << endl;
}

void Circle2::printLength() {
    cout << "Length: " << length << endl;
}

void Circle2::printRadius() {
    cout << "Radius: " << radius << endl;
}