Абстрактный класс function с классами hiperbola, parabola, ellipse

#include <iostream>
using namespace std;
class Function 
{
protected:
    double a, b, c;
public:
    virtual double evaluate(double x) = 0;
    void setParams(double a, double b, double c) {
        this->a = a;
        this->b = b;
        this->c = c;
    }
};
class parabola: public Function
{
public:
    double evaluate(double x)
    {
        return a*x*x + b*x + c;
    }
}; 
class hyperbola : public Function
{
public:
    double evaluate(double x)
    {
        return a/(x-b)+c;
    }
};
class ellipse : public Function
{
public:
    double evaluate(double x)
    {
        return sqrt(a-x*x*b)+c;
    }
};
int main() {
    Function *f;
    double a, b, c;
    cout << "1) ellipse" << endl;
    cout << "2) parabola" << endl;
    cout << "3) hyperbola" << endl;
    cout << "select function (input digit):";
    char ch;
    cin >> ch;
    switch (ch) 
    {
    case '1': f = new ellipse; break;
    case '2': f = new parabola; break;
    case '3': f = new hyperbola; break;
    }
    cout << "input 3 numerical params(double):";
    cin >> a >> b >> c;
    f->setParams(a, b, c);
    cout << "input argument(double):";
    cin >> a;
    cout << "f(" << a << ")=" << f->evaluate(a) << endl;
    cin.get();
    delete f;
    return 0;
}