PAT (Advanced Level) 1104. Sum of Number Segments (20)

#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<map>
#include<queue>
#include<stack>
#include<algorithm>
using namespace std;int n;
double a[+];
double b[+];
double sum=;int main()
{
scanf("%d",&n);
for(int i=;i<=n;i++) b[i]=1.0*(n-i+)*i;
for(int i=;i<=n;i++) scanf("%lf",&a[i]);
for(int i=;i<=n;i++) sum=sum+b[i]*a[i];
printf("%.2lf\n",sum);
return ;
}