Question

I’m attempting to solve the second problem on Project Euler, here is the problem:

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, …

Find the sum of all the even-valued terms in the sequence which do not exceed four million.

So, I have set up the following:

using System;

namespace ProjectEuler
{
    class Question2
    {
        //Project Euler - Question 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, ...
        //Find the sum of all the even-valued terms in the sequence which do not exceed four million
        static void Main()
        {
            int sum = 0;

            int oldNumber = 1;
            int currentNumber = 1;
            int nextNumber;

            while (currentNumber <= 500)
            {
                nextNumber = currentNumber + oldNumber;

                if (nextNumber % 2 == 0)
                {
                    sum += currentNumber;
                }
            }

            Console.WriteLine("Project Euler - Question 2\n\nAnswer: " + sum);
            Console.ReadLine();
        }
    }
}

When I run the program, there is nothing visible, just a cursor in the Windows command line. I think that may be do the fact that currentNumber isn’t getting updated, but I can’t think of how to do that properly, if that even is the case.

Answer 1

You don’t have a condition to end your loop. You never change the value of currentNumber to anything but 1.

You probably want something like:

nextNumber = currentNumber + oldNumber;
oldNumber = currentNumber;
currentNumber = nextNumber;