BSTreeSuccAbove.c

struct node* BSTreeSuccAbove(struct node* p, struct node* x) { 
    struct node* succ = NULL; 
    while (p != x) { 
        if (x->key < p->key) { 
            succ = p; 
            p = p->lft; 
        } else if (x->key > p->key) { 
            p = p->rgt; 
        } 
    } 
    return succ; 
}