c stack queue in deque

#include <stdio.h>
#include <stdlib.h>
#define class(a) typedef struct a a; struct a
#define make(a) (a *)malloc(sizeof(a))

// 双向链表
class(node) {
    int data;          // 数据
    node *prev, *next; // 前后节点
};

// 栈
class(stack) {
    node *top; // 栈顶
};

stack *stack_init(stack *s) {
    s->top = NULL;
    return s;
}

stack *stack_push(stack *s, int data) {
    node *n = make(node);
    *n = (node) { data, s->top, NULL };
    s->top = n;
    return s;
}

int stack_pop(stack *s) {
    node *n = s->top;
    int d = n->data;
    s->top = n->prev;
    free(n);
    return d;
}

void stack_show(stack *s) {
    for (node *p = s->top; p; p = p->prev) {
        printf("%c ", p->data);
    }
    printf("\n");
}

// 队列
class(queue) {
    node *head, *tail; // 队列头尾
};

queue *queue_init(queue *s) {
    s->head = s->tail = NULL;
    return s;
}

queue *queue_push(queue *s, int data) {
    node *n = make(node);
    *n = (node) { data, s->tail, NULL };
    if (s->tail) s->tail->next = n;
    s->tail = n;
    if (!s->head) s->head = s->tail;
    return s;
}

int queue_shift(queue *s) {
    node *n = s->head;
    int d = n->data;
    if ((s->head = n->next)) s->head->prev = NULL;
    free(n);
    if (!s->head) s->tail = NULL;
    return d;
}

void queue_show(queue *s) {
    for (node *p = s->head; p; p = p->next) {
        printf("%c ", p->data);
    }
    printf("\n");
}

// 测试
void test_all(char *string, stack *s, queue *q) {
    static int n_case = 1;
    printf("Case #%d:\n", n_case++);
    for (char *p = string; *p; ++p) {
        s = stack_push(s, *p);
        q = queue_push(q, *p);
    }

    printf("stack: ");
    stack_show(s);
    printf("queue: ");
    queue_show(q);

    while (s->top && q->head && stack_pop(s) == queue_shift(q))
        ;
    if (s->top || q->head)
        printf("not palindrome\n");
    else
        printf("palindrome\n");

    while (s->top) stack_pop(s);
    while (q->head) queue_shift(q);
    printf("\n");
}

int main(void) {
    stack s;
    queue q;

    stack_init(&s);
    queue_init(&q);

    test_all("", &s, &q);
    test_all("a", &s, &q);
    test_all("hello, world", &s, &q);
    test_all("12345678987654321", &s, &q);

    return 0;
}