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