C中for循环求阶乘的和

Question

#include<stdio.h>

int main()
{
int i,n;
double fac=1,sum=0;
scanf("%d",&n);
for(i=1; i<=n; i++)
{
fac=fac*i;
sum=sum+fac;
}
printf("%d\n",sum);
return 0;
}
为啥不能实现

Answer 1

sum是double类型的，输出用%lf

Answer 2

double类型对应输出用%lf

Answer 3

修改后d代码

#include<stdio.h>

int main()
{
    int i,n;
    double fac=1,sum=0;
    scanf("%d",&n);
    for(i=1; i<=n; i++)
    {
        fac = fac*i;
        sum = sum + fac;
    }
    printf("%lf\n",sum);
    return 0;
}

Answer 4

lf