cppPolygonClassDemo

#include <iostream>
#include <vector>
#include <string>
#include <math.h>

class Polygon
{
protected:
    std::vector<float> sides;
public:
    Polygon& addSide(float side) { sides.push_back(side); return *this; }
    Polygon& setSide(int sideId, float side)
    {
        sides[sideId] = side;
        return *this;
    }
    float getSide(int sideId)const { return sides[sideId]; }

    virtual float perimeter() const
    {
        float per{ 0 };
        for (const auto& side : sides) { per += side; }
        return per;
    }

    virtual float area()const = 0;

    const Polygon& sidesInfo() const
    {
        for (int i{ 0 }, maxSides{ (int)sides.size() }; i < maxSides; ++i)
        {
            std::cout << " Side " << char('A' + i) << " is " << sides[i] << " long\n";
        }
        return *this;
    }

    std::string name() const
    {
        std::string nm{ typeid(*this).name() };
        return nm.substr(5);
    }

    const Polygon& info()
    {
        std::cout << name() << ":\n"
            << " Perimeter: " << perimeter()
            << " Area " << area() << '\n';
        sidesInfo();
        std::cout << '\n';

        return *this;
    }
};

class Rectangle : public Polygon
{
public:
    Rectangle(float sideA, float sideB) { addSide(sideA); addSide(sideB); }
    virtual float perimeter()const override { return Polygon::perimeter() * 2; }
    virtual float area()const override { return getSide(0) * getSide(1); }
};

class Square : public Rectangle
{
public:
    Square(float sideA) : Rectangle{ sideA, sideA } {};
};

class Triangle : public Polygon
{
public:
    Triangle(float sideA, float sideB, float sideC)
    {
        addSide(sideA).addSide(sideB).addSide(sideC);
    }

    virtual float area()const override
    {
        const float p{ perimeter() / 2 };
        return sqrt(p * (p - getSide(0)) * (p - getSide(1)) * (p - getSide(2)));
    }
};

int main()
{
    //Polygon* polygons[]{ new Rectangle{4,5}, new Square{6}, new Triangle{3,4,5} };

    Rectangle rectangle{ 4,5 };
    Square square{ 6 };
    Triangle triangle{ 3,4,5 };

    Polygon* polygons[]{ &rectangle, &square,  &triangle};

    for (const auto& polygon : polygons)
    {
        polygon->info();
        //delete polygon;
    }

    return 0;
}