A ring in C

ref_ring.c

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

struct ring_int {
  struct ring_int *next;
  int value;
} ring_int;

struct ring_int *new_ring(int capacity, int placeholder);

void advance(struct ring_int **ring);

void test_two_rounds(struct ring_int *ring, int *expected, int len);

int main() {
  struct ring_int *ring = new_ring(3, 0);
  int expected_0[3] = {0, 0, 0};

  test_two_rounds(ring, expected_0, 3);

  int expected[3] = {1, 2, 3};

  for (int i = 0; i < 3; i++) {
    ring->value = expected[i];
    advance(&ring);
  }

  test_two_rounds(ring, expected, 3);
}

struct ring_int *new_ring(int capacity, int placeholder) {
  struct ring_int *cur = (struct ring_int *)malloc(sizeof(struct ring_int *));
  struct ring_int *start = cur;

  for (int i = 1; i < capacity; i++) {
    struct ring_int *next =
        (struct ring_int *)malloc(sizeof(struct ring_int *));

    cur->next = next;
    cur = next;
  }

  cur->next = start;

  return start;
}

void advance(struct ring_int **ring) { *ring = (*ring)->next; }

void test_two_rounds(struct ring_int *ring, int *expected, int len) {
  for (int i = 0; i < 2 * len; i++) {
    if (ring->value != expected[i % len]) {
      printf("val: %d\texpected[%d]: %d\n", ring->value, i % len,
             expected[i % len]);
      exit(i + 1);
    }
    advance(&ring);
  }

  printf("Test passed\n");
}