Code is giving absurd answer

Question

The following code segement is to calculate sum(K*((nCk)^2)) for 1<=k<=n and for n till 10^6, but the program starts giving absurb answer for n>20. Please help me. I think it may be because the product is not able to store such large value but what to do?

#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
int main()
{
    int t;
    scanf("%i",&t);
    while(t--)
    {
        int n;
        scanf("%i",&n);
        double prod=1;
        if (n!=1)
        {
            for(float i=1;i<n;i++)
            {
                prod = prod * (2+(i/(n-i))) ;
                prod = fmod(prod,1000000007.0);
            }
            prod = prod * n; 
        }
        else prod=1 ;   
        prod = int(prod)%1000000007;
        cout<<prod;
        printf("\n");
        }
    return 0;
}

Answer 1

You are doing

prod = prod * (2+(i/(n-i))) ;

You will lose precision when (i/(n-1)) is not integral and gives recurring decimal number. This will lead to unexpected results.