Project Euler - Problem 2

problem2.c

#include <cs50.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/*  
    Even Fibonacci Numbers

    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.
*/

//prototype
int fib(int x);

int main(void)
{
    int n = 4000000;
    int sum = 0;
    
    for(int i = 1; i < 34; i++)
    {
        if (fib(i) <= n)
        {
            if (fib(i) % 2 == 0)
                sum += fib(i);
        }
    }
    printf("Final sum = %i\n", sum);
}

// returns next fibonacci number
int fib(int x)
{
    if (x == 0)
        return 0;
    else if (x == 1)
        return 1;
    else
        return (fib(x-1) + fib(x-2));
}