C++ - ProjectEuler.net, Problem 2
=================================

Public domain    
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    /*
     * projecteuler.net, Problem 2 :
     * 
     * By considering the terms in the Fibonacci sequence whose values do not 
     * exceed four million, find the sum of the even-valued terms. 
     *
     * 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 <iomanip>
    
    using namespace std;
    
    main()
    {
        const int max = 4000000;
        int sum = 0;
    
        for (int i = 1, j = 1; i < max; i += j) {
                // check for even number
                if (i % 2 == 0) {
    
                        // print plus sign before every number
                        // except the first one
                        if (sum != 0)
                                cout << " + ";
    
                        cout << i;
                        sum += i;
                }
    
                // swapping two variables
                i -= j += i -= j = -j;
    
        }
    
        cout << " = " << sum << endl;
    }

Output :

    2 + 8 + 34 + 144 + 610 + 2584 + 10946 + 46368 + 196418 + 832040 + 3524578 = 4613732

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_BY: Pejman Moghadam_  
_TAG: cpp, mathematics, projecteuler_  
_DATE: 2011-09-23 17:32:37_