#include <stdio.h>

class BadAddition
{
private:
    float q1, q2;
public:
    BadAddition (float q1, float q2) :
        q1 (q1),
        q2 (q2)
    {}

    float Get1 () const
    {
        return q1;
    }

    float Get2 () const
    {
        return q2;
    }
};

class FloatSequence
{
private:
    float a0;

public:
    FloatSequence (float a0) :
        a0 (a0)
    {}

    virtual float Elem (int idx) const = 0;

    float operator[] (int idx)
    {
        if (idx == 0)
            return a0;
        else
            return Elem (idx);
    }
};

class GeometricSequence : public FloatSequence
{
private:
    float a0, q;
public:
    GeometricSequence (float a0, float q) :
        FloatSequence(a0),
        q (q)
    {}

    GeometricSequence operator+ (const GeometricSequence& op2) const
    {
        if (q == op2.q)
        {
            GeometricSequence res (a0 + op2.a0, q);
            return res;
        }
        else
            throw BadAddition (q, op2.q);
    }

    float Elem (int idx) const
    {
        int res = a0;

        for (int i = 0; i < idx; i++)
        {
            res = res * q;
        }

        return res;
    }
};

int main ()
{
    try
    {
        GeometricSequence a (1, 2);
        GeometricSequence b (0.25, 2);
        GeometricSequence c (16, 0.5);
        printf ("%3.3f %3.3f %3.3f\n", a[0], b[3], c[2]);
        printf ("%3.3f\n", (a+b) [1]);
        printf ("%3.3f\n", (b+c) [1]);
    }
    catch (const BadAddition &x)
    {
        printf ("Bad addition: %3.3f %3.3f\n", x.Get1(), x.Get2());
    }
    return 0;
}