#include <stdlib.h>

struct _queue 
{
    void *data;
    struct _queue *next;
};

typedef _queue queue;

queue queue_allocate(void *value)
{
    queue *node = malloc(sizeof(queue));
    if (node)
    {
        node->data = val;
        node->next = NULL;
    }
    return node;
}

void queue_free(queue *node)
{
    if (node)
    {
        free(node);
    }
}

void queue_append(queue **head, void *value) 
{
    if ((*head)->next == NULL)
    {
        (*head)-> = value;
    }
    else
    {
        queue *cur;
        for (cur = (*head)->next; cur->next != NULL; cur = cur->next);
        cur->next = item;
    }
}

void queue_pop(queue **head)
{
    int value = (*head)->data;
    queue *tmp = (*head)->next;
    free(*head);
    head = tmp;
}

void queue_display(queue *head)
{
    queue *cur;
    for (cur = head->next; cur->next != NULL; cur = cur->next)
    {
        fprintf(stdout, "%s\n", cur->data);
    }
}

void main(void)
{
    queue *main;
    //...
}