Converting an iterative function to recursive

Question

I know people usually ask this question the other way round, but I have the following problem: I have this iterative function which counts all the nodes in a circular doubly

Answer 1

int count(struct node * ptr)
{
    return ptr==NULL ? 0 : (ptr->roll_no == 20 ? 1:0) + count(ptr->next);
}

UPDATE: it appears the list is circular.

int count(struct node * start, struct node * ptr)
{
    return ptr==NULL || ptr->next == start ? 0 
                                           : (ptr->roll_no == 20 ? 1:0) 
                                             + count(start, ptr->next);
}
/* to be called like: */
cnt = count (the_list, the_list);

UPDATE 2: (failure to count the last node)

int count(struct node * start, struct node * ptr)
{
    return ptr==NULL  ? 0 
                      : (ptr->roll_no == 20 ? 1:0) 
                        + ptr->next == start ? 0
                                             : count(start, ptr->next);
}

UPDATE3: it did need an extra pair of parentheses...

#include 

struct node {
        struct node *next;
        int roll_no;
        };

struct node nodes[8] =
{{ nodes+1, 20} ,{ nodes+2, 0}
,{ nodes+3, 20} ,{ nodes+4, 0}
,{ nodes+5, 20} ,{ nodes+6, 0}
,{ nodes+7, 20} ,{ nodes+0, 0}
};

unsigned count(struct node * start, struct node * ptr)
{
    return ptr==NULL
              ? 0
              : (ptr->roll_no == 20 ? 1:0)
                + (ptr->next == start
                    ? 0
                    : count(start, ptr->next)
                  )
              ;
}

#define COUNT(p) count(p,p)

int main (void)
{
unsigned cnt,idx;

for (idx = 0; idx < 8 ; idx++) {
    cnt = COUNT (nodes+idx);
    printf ("count@%u = %u\n", idx, cnt);
    }

return 0;
}