#include
int main()
{
int i,k,n,t;
double ans;
scanf("%d",&n);
ans = 0;
t = 1;
k = 1;
for(i = 1; i 输入输出示例Enter n;3sum=0.893要这个版式，谢谢#includeint main(){int i, k, n, t;double ans;printf("Enter n:");scanf("%d", &n);ans = 0;t = 1;k = 1;for(i = 1; i <= n; ++i){ans += (double)t / k;k += 3;t *= -1;}printf("sum=%.3lf\n", ans);return 0;}