c语言级数计算，误差由用户输入

Question

1-1/2！+1/3！-1/4！+1/5.....=

Answer 1

#include<stdio.h>
#include<math.h>
int main() {
    double a,i=1,sum=0,t=1,up=1,term=1;
    printf("Input eps:");
    scanf("%lf",&a);
    while(fabs(t/up)>=a){
        sum+=t/up;
        t=-t;
        i++;
        up=up*i;
    }
    sum+=t/up;
    printf("%.8f",sum);
    return 0;
}.