void stack_realloc (struct Stack * s);

struct Stack *stack_create(int size)
{
    struct Stack *s;
    s = (struct Stack *) calloc (1, sizeof (struct Stack));
    s->a = (Data *) calloc (size, sizeof (Data));
    s->n = 0;
    s->size = size;
    return s;
}

void stack_push(struct Stack * s, Data x)
{
    if (s->n >= s->size)
        stack_realloc (s);
    if (s->n < s->size) {
        s->a[s->n] = x;
        s->n++;
    }
}

Data stack_pop(struct Stack * s)
{
    if (s->n > 0) {
        s->n--;
        return s->a[s->n];
    }
    return -1;
}

Data stack_get(struct Stack * s)
{
    if (s->n > 0)
        return s->a[s->n - 1];
    return -1;
}

void stack_print(struct Stack * s)
{
    if (s->n == 0) {
        printf ("Empty stack\n");
        return;
    }
    for (size_t i = 0; i < s->n; i++) {
        printf ("%d ", s->a[i]);
    }
    printf ("\n");
}

int  stack_size(struct Stack * s)
{
    return s->n;
}

void stack_clear(struct Stack * s)
{
    s->n = 0;
    for (size_t i = 0; i < s->size; i++)
        s->a[i] = 0;
}

void stack_destroy(struct Stack * s)
{
    s->n = 0;
    free (s->a);
    free (s);
}

void stack_realloc (struct Stack * s)
{
    Data *na = (Data *) calloc (s->size * 2, sizeof (Data));
    for (int i = 0; i < s->size; i++)
        na[i] = s->a[i];
    free (s->a);
    s->a = na;
    s->size = 2 * s->size;
}

int  stack_is_empty(struct Stack * s)
{
    if (s->n == 0) return 1;
    return 0;
}