from ch2 of Elements of Programming

transformations.cpp

/** Chapter 2 of "Elements of Programming": Transformations
 */

#define DistanceType(F) int
#define Domain(F) int
#define pointer(T) *T

template<typename T>
class Transformation {
    public:
        Transformation() {};
        virtual T operator() (T x) = 0;
};

template<typename T>
class Square : public Transformation<T> {
    public:
        virtual T operator() (T x) { return x * x; }
};


DistanceType(F) distance(Domain(F) x, Domain(F) y, Square<int> f) {
    typedef DistanceType(F) N;
    // Precondition: y is reachable from x under f
    N n(0);
    while(x != y) {
        x = f(x);
        n += 1;
    }
    return n;
}

#include <iostream>
using namespace std;
int main() {
    int x = 2;
    int y = 256;
    Square<int> f = Square<int>();
    int d = distance(x, y, f);
    cout << "the distance between " << x << " and " 
         << y << " is " << d << endl;

    return 0;
}