Problem2-Project Euler

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.

找出400 0000以下斐波那契数中的偶数求和，累加即可（用递推公式，通项公式可能有舍入误差）

#include"stdio.h"

int main()        /*problem2-Even Fibonacci numbers*/
{
    int a[100]={1,1,2},i;
    double sum=0;
    for(i=3;;i++)
    {
        a[i]=a[i-2]+a[i-1];
        if(a[i]>4000000.0||i==100)
            break;
    }
    for(i=2;a[i]!=0;i+=3)
        sum+=a[i];
    printf("sum is %lf\n",sum);
    return(0);
}