sigsegv error.

// program for codechef UNCLE JOHNY

#include <stdio.h>

int main()
{
    int t,pos,i,ujp,j;
    unsigned long int n;
    int arr[n];
    int high=n,low=0,mid;
    scanf("%d",&t);
    while (t)
    {
        scanf ( "%ld",&n);
        low=0;
        high=n;
        mid=(high+low)/2;
        for (i=0; i<n; i++ )
        {
            scanf("%d",&arr[i]);
        }
        scanf ("%d",&ujp); //pos. pf uj in unsorted array
        //uj=arr[ujp-1];
        for (j=0; j<n-1 ; j++)
        {
        for (i=0; i<n-1-j; i++)
        {
            if ( arr[i]>arr[i+1] )
            {
                arr[i]=arr[i]+arr[i+1];
                arr[i+1]=arr[i]-arr[i+1];
                arr[i]=arr[i]-arr[i+1];

            }

        }
        }

        while ( low<=high )
        {
            if ( arr[mid]==arr[ujp])
            {
                pos=mid;
                break;
            }
            else if ( arr[mid] > arr[ujp] )
            {
                high=mid-1;
                mid=(low+high)/2;

            }
            else
            {
                low=mid+1;
                mid=(low+high)/2;

            }

        }

        printf("%d\n",pos+1 );
        t--;

    }
}

plzz guys....tell me where is the segmentation fault.