#include <iostream.h>

class Plant {
public:
    Plant(int init_a) : a(init_a) {}
    virtual int leaf(int x) { return x * a; }
    int stem(int x) { return x * leaf(x); }
private:
    int a;
};

class Tree : public Plant {
public:
    Tree(int init_a, int init_b)
        : Plant(init_a), b(init_b) {}
    virtual int leaf(int x) { return x * b; }
    int stem(int x) { return x * leaf(b); }
    virtual int trunk(int x) { return x * stem(x); }
private:
    int b;
};

class Moss : public Plant {
public:
    Moss(int init_b) : Plant(0), b(init_b) {}
    int stem(int x) { return b; }
    virtual int leaf(int x) { return x * stem(x); }
private:
    int b;
};

int main()
{
    Plant p(3);
    Tree t(20,50);
    Moss m(-4);

    // Illegal : no such constructor
    // Moss n(0,1);

    Plant * p_ptr = &t;
    Plant * q_ptr = &m;

    // Illegal: downcast to subclass pointer not permitted
    // Tree * t_ptr = p_ptr;
    Tree * u_ptr = &t;

    // Illegal: no trunk method defined on plant class.
    // cout << p_ptr->trunk(3) << endl;
    cout << u_ptr->trunk(3) << endl;

    // Note that Plant::stem() has a virtual call to leaf(), resulting
    // in a call to Tree::leaf().
    cout << p_ptr->stem(4) << endl;

    return 0;
}