c语言 求以下数列的和S

Question

输入a和n S=1/a-2/两个a+3/三个a

+（-1）的n-1次方乘n/n个a （n小于10

Answer 1

供参考：

#include <stdio.h>
int main()
{
    int a,n,i = 1,t = 0,k = 1;
    double s = 0;
    scanf("%d%d",&a,&n);
    while (n--){
          t = t * 10 + a;
          s += i * k * 1.0/ t;
          i++;
          k *= (-1);
    }
    printf("%f",s);
    return 0;
}