C语言，计算1/3-3/4+4/7-7/11+11/18-18/29+……前n项的和，n的值在程序运行时输入。

Question

#include<stdio.h>
#include<math.h>
int main()
{
int n, i, shang=1, xia=3, sum = 0, temp;
sum = shang / xia;
printf("请输入n的值:");
scanf("%d", &n);
for (i = 2; i <n;i++)
{
temp = shang;
shang = xia;
xia = shang + temp;
sum = sum + shang / xia * pow(-1, i - 1);
}
printf("前%d项和为%d\n", n, sum);
}
哪里错了鸭？要怎么改正鸭？

Answer 1

shang xia sum temp应该是double 类型

#include <stdio.h>
#include <math.h>
int main()
{
    int n, i;
    double  shang = 1, xia = 3, sum = 0, temp; //shang xia sum temp应该是double 类型
    sum = shang / xia;
    printf("请输入n的值:");
    scanf("%d", &n);
    for (i = 2; i <= n; i++) // 是 i <= n;
    {
        temp = shang;
        shang = xia;
        xia = shang + temp;
        sum = sum + shang / xia * pow(-1, i - 1);
    }
    printf("前%d项和为%lf\n", n, sum);
}

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