Provides a way to iterate over the Fibonacci sequence.

Fibonacci.cpp

//===----------------------------------------------------------------------===//
//
// NAME         : FibonacciGenerator
// VERSION      : 0.2
// NAMESPACE    : Global namespace.
// PURPOSE      : Provided a way to iterate over the Fibonacci sequence.
// COPYRIGHT    : (c) 2012 Sean Donnellan. All Rights Reserved.
// AUTHORS      : Sean Donnellan ([email protected])
// DESCRIPTION  : Provided a way to iterate over the Fibonacci sequence.
//
//                Supports ++, != and * operators.
//
//                Example usage:
//                  FibonacciGenerator g;
//                  This will print out the first 10 Fibonacci numbers.
//                    std::for_each(FibonacciGenerator::begin(),
//                                  FibonacciGenerator::end(10),
//                                  [](int fib){
//                                    std::cout << fib << " ";
//                                  });
//
//                  This makes it incrediablity easy if you want to know
//                  the sum of the first 10 Fibonacci numbers.
//                    std::accumulate(FibonacciGenerator::begin(),
//                                    FibonacciGenerator::end(10),
//                                    0);
//
//===----------------------------------------------------------------------===//
class FibonacciGenerator
{
  // last and secondlast is used in the calcuations.
  unsigned long last;
  unsigned long secondlast;

  // This is used for dealing with iteration.
  // n keeps track of the which 'n'-th Fibonacci number we are up to.
  unsigned int n;

  FibonacciGenerator(unsigned int n);

public:

  FibonacciGenerator& operator ++();

  // Returns the 'n-th' fibonacci number.
  unsigned long operator *() const;

  bool operator !=(const FibonacciGenerator& That) const;

  // Starts at the beging of the sequence.
  static FibonacciGenerator begin();

  // Defines the termination case.
  // Note: Deferencing this is meaninless, it is mearly a terminator.
  static FibonacciGenerator end(unsigned int nth);
};

//===----------------------------------------------------------------------===//

FibonacciGenerator::FibonacciGenerator(unsigned n)
: last(1), secondlast(0), n(n)
{
}

FibonacciGenerator& FibonacciGenerator::operator ++() {
  last = last + secondlast;
  secondlast = last - secondlast;
  ++n;
  return *this;
}

unsigned long FibonacciGenerator::operator *() const {
  return secondlast;
}

bool FibonacciGenerator::operator !=(const FibonacciGenerator& That) const {
  return n != That.n;
}

FibonacciGenerator FibonacciGenerator::begin() {
  return FibonacciGenerator(0);
}

FibonacciGenerator FibonacciGenerator::end(unsigned int nth) {
  return FibonacciGenerator(nth);
}

//===----------------------------------------------------------------------===//

#include <algorithm>
#include <iostream>
#include <numeric>

int main()
{
  std::cout << "Fibonacci: ";
  std::for_each(FibonacciGenerator::begin(), FibonacciGenerator::end(10),
                [](int fib){ std::cout << fib << " "; });

  std::cout << std::endl;

  std::cout << "Sum of first 10 Fibonacci numbers: "
            << std::accumulate(FibonacciGenerator::begin(),
                               FibonacciGenerator::end(10), 0)
            << std::endl;
  return 0;
}
//===----------------------------------------------------------------------===//