How can you find an element using binary search on a recursive function C?

Question

I wrote this shortcode to find element x location in a sorted array (from high to low) with complexity O(log n). n and arr represent the edges of the array. However, it doesn't seem to work properly. Any suggestions?

int ex2_1(int *arr, int n, int key)
{
    if (n == 0)
        return -1;
    if (arr[n / 2] == key)
        return n / 2;
    if (arr[n / 2] > key)
        return ex2_1(arr + n / 2 + 1, n - n / 2 - 1, key);
    return ex2_1(arr, n / 2, key);
}

for int arr[] = { 9, 7, 7, 5, 3, 3, 3, 1 };, int n = 8 and int key = 3, I get 4 when I should get 5.

Answer 1

After optimization of chqrlie's code I got to this, and it works well:

int ex2_1(int* arr, int n, int key)
{
    if (n == 0) return -1;
    if (arr[n/2] == key) return n / 2;
    if (arr[n/2] > key)
    {
        int a = ex2_1(arr + n/2 + 1, n - n/2 - 1, key);
        if (a == -1) return -1;
        return n / 2 + 1 + a;
    }
    return ex2_1(arr, n/2, key);
}