Q10014: Simple calculations

// Run time: 0.010
#include <stdio.h>
int main()
{
   int num; // 輸入組數
   int n;
   int i;  // for loop count
   int weight;
   double s, e; // a(0) and a(n+1)
   double sum, total;

   scanf("%d", &num);

   while (num--)
   {
       sum = total = weight = 0;

       scanf("%d", &n);
       scanf("%lf%lf", &s, &e);

       double arr[n];
       for ( i = 0; i < n; i++)
           scanf("%lf", &arr[i]);

       sum = s*n+e;

       for ( i = n-1; i >= 0; i--)
           total += (weight+=2)*arr[i];

       printf("%.2lf\n", (sum-total)/(n+1));

       if (num)
           printf("\n");
   }

   return 0;
}