// File: ex7-5.cpp

#include <iostream>
#include <cmath>
using namespace std;

class Triangle
{
protected:
    double a,b,c;
public:
    Triangle(double s1,double s2,double s3) : a(s1), b(s2), c(s3) {}
    double area()const;
    double perimeter() const
    {
        return a + b + c;
    }
    friend ostream& operator<<(ostream&, const Triangle&);
};

double Triangle::area() const
{
    double s = perimeter()/2.0;	//	s = semiperimater
    return sqrt(s*(s-a)*(s-b)*(s-c));
}

ostream& operator<<(ostream& out, const Triangle& triangle)
{
    out << &triangle << ": sides "
        << triangle.a << ' ' << triangle.b << ' ' << triangle.c;
    return out;
}

class Isosceles : public Triangle
{
public:
    Isosceles(double base, double leg) : Triangle(base,leg,leg) {}
};

class Equilateral : public Isosceles
{
public:
    Equilateral(double side) : Isosceles(side,side) {}
};


int main()
{
    Triangle t1(3,4,5);
    cout << t1 << endl;
    cout << "perimeter=" << t1.perimeter() << "  area=" << t1.area() << endl;

    Isosceles t2(2,4);
    cout << t2 << endl;
    cout << "perimeter=" << t2.perimeter() << "  area=" << t2.area() << endl;

    Equilateral t3(5);
    cout << t3 << endl;
    cout << "perimeter=" << t3.perimeter() << "  area=" << t3.area() << endl;

}