菜鳥OJ， C語言數簡單列求和， 感覺測試沒錯， 但是wrong answer， 求大神指點

Description
有一個分數序列：2/1，3/2，5/3，8/5，13/8，21/13... 求出這個數列的前n項之和。

Input
多測試用例，每個測試用例一行，每行是一個正整數n

Output
為每個測試用例單獨輸出一行：該數列的前n項之和。結果均保留小數點後10位。

Sample Input
1
2
3

Sample Output
2.0000000000
3.5000000000

5.1666666667

#include
int main(void){
double i, n, j, x, sum, tem, x1, x2, y1, y2, y;
while(scanf("%lf", &n)!=EOF&&n>=0){
x1=2; x2=3; y1=1; y2=2; sum=0;

if(n==0) sum=-3.5;
else if(n==1) sum=-1.5;
else if(n==2) sum=0;
else
for(i=1; i<=n-2; i++){
x=x1+x2; x2=x1; x1=x; y=y1+y2; y2=y1; y1=y;
sum=sum+x/y;
}

printf("%.10f\n", sum+3.5);
}
return 0;
}

OJ反饋信息：wrong answer

最佳回答：

不知道你寫的為啥不對，我寫了一個，c語言的

 struct Node
{
    double number;
    Node* pNext;
    Node()
    {
        number = 0;
        pNext = NULL;
    }
};
int main()
{
    int n = -1;
    Node* pNode = new Node;
    Node* pHead = pNode;
    Node* pPre = pNode;
    while (scanf_s("%d", &n) != EOF)
    {
        pNode->number = n;
        Node* pNext = new Node;
        pNode->pNext = pNext;
        pPre = pNode;
        pNode = pNext;
    }

    delete pNode;
    pPre->pNext = NULL;
    pNode = pHead;
    double sum = 0.0;
    while (pNode->pNext != NULL)
    {
        double d = pNode->pNext->number / pNode->number; 
        sum += d;
        printf("%.10f\n", sum);
        pNode = pNode->pNext;
    }

    return 0;
    }