Triangle

//ITriangle.h
class ITriangle
{
    public:
    virtual double GetArea();
    virtual bool IsRightTriangle();
    virtual bool IsEquilateralTriangle();
    virtual bool IsIsoscelesTriangle();
}

//CTriangle.cpp
#include "ITriangle.h"

class ThreeSidesTriangle : ITriangle
{
    private:
    double Side1;
    double Side2;
    double Side3;

    public:
    ThreeSidesTriangle()
    {
        Side1 = Side2 = Side3 = 0.0;
    }

    ThreeSidesTriangle(double side1, double side2, double side3) : Side1(side1), Side2(side2), Side3(side3)
    {

    }

    double GetArea()
    {
        //Do the stuff to compute the area and return it
    }

    bool IsRightTriangle() { /*...*/ }

    bool IsEquilateralTriangle()
    {
        return Side1 == Side2 && Side1 == Side3;
    }

    bool IsIsoscelesTriangle() { /*...*/ }
}