0002_even_fibonacci_numbers.cpp

/**********************
Author: Daniel Bowder
Date: July 16, 2018

Problem: https://projecteuler.net/problem=2
  "Each new term in the Fibonacci sequence is generated by adding the previous two terms.
   By starting with 1 and 2, the first 10 terms will be:
   1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
   By considering the terms in the Fibonacci sequence whose values do not exceed four million,
   find the sum of the even-valued terms."

***********************/

#include <iostream>
#include <cmath>

using std::cout;
using std::endl;

long double even_fibonacci_numbers(long double valueMax) {
  // Setup our sum variable to add our conditional Fibonacci Numbers to.
  long double sum = 0;
  // Setup our Fibonacci numbers.       valueA = n     valueB = (n - 1)
  double valueA = 1;
  double valueB = 1;
  //    ** Value B will hold the valueA from the prior calculation, so that,
  //    in the spirit of the Fibonacci sequence, we can add the current value,
  //    to the prior value in the sequence.

  // Setup our temprary variable to hold valueA, later to transfer to valueB.
  double valueTemp;

  for (int i=0; valueA < valueMax; i++) {

    // If Fibonacci Number is evenly divisible by 2,
    if (0 == fmod(valueA, 2)) {
      // add the current Fibonacci Number to the sum.
      sum = sum + valueA;
    }

    // Incriment the Fibonacci Counter
    valueTemp = valueA;           // Store valueA so that we can update valueA.
    valueA = valueA + valueB;     // Update valueA
    valueB = valueTemp;           // Assign valueB to the value of valueA before we updated valueA.
  }

  return sum;
}


int main(int argc, char* argv[]) {
  cout << "Problem 2. " << even_fibonacci_numbers(4000000) << endl;
}