C++ interface (pure abstract class) && C# interface

1- C# Interface

public interface IShape
{
    double Area();
    double Perimeter();
}

2- C# Implementation (Rectangle)

public class Rectangle : IShape
{
    private readonly double width;
    private readonly double height;

    public Rectangle(double width, double height)
    {
        this.width = width;
        this.height = height;
    }

    public double Area() => width * height;

    public double Perimeter() => 2 * (width + height);
}

3- Using the C# interface

IShape shape = new Rectangle(3.0, 4.0);
Console.WriteLine($"Area: {shape.Area()}");
Console.WriteLine($"Perimeter: {shape.Perimeter()}");

A- C++ Interface (pure abstract class)

class IShape {
public:
    virtual ~IShape() = default;        
    virtual double area() const = 0;    
    virtual double perimeter() const = 0; 
};

B- C++ Implementation of the Interface

class Rectangle : public IShape {
public:
    Rectangle(double width, double height)
        : w_(width), h_(height) {}

    double area() const override {
        return w_ * h_;
    }

    double perimeter() const override {
        return 2 * (w_ + h_);
    }

private:
    double w_;
    double h_;
};

C- Using the Interface in C++

#include <iostream>
#include <memory>

int main() {
    std::unique_ptr<IShape> shape = std::make_unique<Rectangle>(3.0, 4.0);

    std::cout << "Area: " << shape->area() << "\n";
    std::cout << "Perimeter: " << shape->perimeter() << "\n";
}