SUMTRAIN-Getting runtime error

I have been working on the SUMTRAIN problem. I used the approach mentioned here. Following is the code that I have come up with.

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int t,n,a,b,e,f,g;
    cin>>t;
    while(t--)
    {
        cin>>n;
        int arr[n][n];
        for(a=0;a<n;a++)
            for(b=0;b<=a;b++)
                cin>>arr[a][b];
        if(n==1)
            cout<<arr[0][0]<<endl;
        else if(n==2)
        {
            if(arr[1][0]>arr[1][1])
                cout<<arr[0][0]+arr[1][0]<<endl;
            else
                cout<<arr[0][0]+arr[1][1]<<endl;
        }
        else
        {

            while(n--)
            {

                int d[(n-1)*2];
                for(e=0;e<((n-1)*2);e++)
                {
                    d[e]=arr[n-1][f]+arr[n-2][e-f];
                    if(e%2==0)
                        f++;
                }
                sort(d,d+(sizeof(d)/sizeof(int)));
                reverse(d,d+(sizeof(d)/sizeof(int)));
                for(g=0;g<(n-1);g++)
                    arr[n-2][g]=d[g];

                cout<<arr[0][0]<<endl;
            }
        }

    }


    return 0;
}

I am not getting solutions for any n>2. What could be the problem?