Problem 2 ---- euler

Even Fibonacci numbers
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.
斐波那契数列中每一个新的项都是前两个项的和。从1和2开始，前10个项是：
1，2，3，5，8，13，21，34，55，89，...

考虑斐波那契数列的项不超过400万，求所有偶数项的和。

#include 
#include 

int main(int argc, char *argv[])
{
        int N;
        scanf("%d", &N);
        int fibona = 2, fibona_1 = 1, fibona_2 = 2, sum = 0;
        while(fibona < N ) 
        {   
                if(fibona % 2 == 0) sum += fibona;
                fibona = fibona_1 + fibona_2;
                fibona_1 = fibona_2;
                fibona_2 = fibona;
        }   

        printf("%d \n", sum);
        return 0;
}

此题重点在于斐波那契数列，教材上一般都拿这个数列来说明递归，但是设置两个中间变量可以避免递归，在实际应用中一般都会避免递归。