Delete a Value from a Circular Linked List

#include <stdio.h>
#include <stdlib.h>

struct CNode { int data; struct CNode *next; };

struct CNode *new_cnode(int value)
{
    struct CNode *node = malloc(sizeof *node);
    if (node == NULL) exit(EXIT_FAILURE);
    node->data = value; node->next = node;
    return node;
}

void cappend(struct CNode **tail, int value)
{
    struct CNode *node = new_cnode(value);
    if (*tail == NULL) { *tail = node; return; }
    node->next = (*tail)->next;
    (*tail)->next = node;
    *tail = node;
}

void cprint(const struct CNode *tail)
{
    if (tail == NULL) { putchar('\n'); return; }
    const struct CNode *current = tail->next;
    do { printf("%d ", current->data); current = current->next; } while (current != tail->next);
    putchar('\n');
}

void cfree(struct CNode *tail)
{
    if (tail == NULL) return;
    struct CNode *head = tail->next;
    tail->next = NULL;
    while (head != NULL) { struct CNode *next = head->next; free(head); head = next; }
}

void delete_cvalue(struct CNode **tail, int key)
{
    if (*tail == NULL) return;
    struct CNode *previous = *tail, *current = (*tail)->next;
    do {
        if (current->data == key) {
            if (current == previous) *tail = NULL;
            else {
                previous->next = current->next;
                if (current == *tail) *tail = previous;
            }
            free(current);
            return;
        }
        previous = current; current = current->next;
    } while (current != (*tail)->next);
}

int main(void)
{
    struct CNode *tail = NULL;
    cappend(&tail, 10); cappend(&tail, 20); cappend(&tail, 30);
    delete_cvalue(&tail, 20);
    cprint(tail);
    cfree(tail);
    return 0;
}