recursive binary search not working properly

Question

int BinarySearch(int A[], int p, int r, int value)
{
    int q = (p + r) / 2;

    if (A[q] == value)
    {
        return q;   //value found
    }
    if (p == q) 
    {
        return 0;   //not found
    }
    if (A[q] > value)
    {
        return BinarySearch(A, p, q, value);
    }
    else
    {
        return BinarySearch(A, q + 1, r, value); 
    }
} //binary search ends here

Now, the problem is that whenever I want to search the last element of an array, this code gives an error. can anyone please explain why?

Answer 1

Make the search end case based on first index p and last index r,

int BinarySearch(int A[], int p, int r, int value)
{
    int q = (p + r) / 2;
    if( p > r )
    {
      return 0;
    }
    if (A[q] == value)
    {
        return q;   //value found
    }
    if (A[q] > value)
    {
        return BinarySearch(A, p, q-1, value);
    }
    else
    {
        return BinarySearch(A, q + 1, r, value); 
    }
}