int BinarySearch(const apvector<int> & list, int target)
// This function uses a Binary Search to search an array
//  ('list') of integers for a specific element ('target').
//  Once found, the index of the element is returned.
//  If 'target' is not found, -1 is returned.

//  Remember that the first element in an array is
//  in position 0, not position 1.

//  NOTE:  For the binary search to work properly, the
//         list MUST already be sorted.
{
   int left=0, right=list.length()-1, middle;
   int place = -1;

   while (left <= right)
   {
      middle = (left + right) / 2;  // Find index of middle element
                                    //  between 'left' and 'right'
      if (target > list[middle])
         left = middle + 1;
      else if (target < list[middle])
         right = middle - 1;
      else
         return middle;             // 'target' must be equal to list[middle]
   }

   return place;
}