链队列的实现

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

typedef struct Node{
	int data;
	struct Node *next;
}node;

typedef struct{
	node head;
	node tail;
	int num; //队列元素个数
}queue;

void queue_init(queue *ps)
{
	ps->head.next = &(ps->tail);
	ps->tail.next = NULL;
	ps->num = 0;
}

void queue_delete(queue *ps)
{
	node *first = NULL, *mid = NULL, *last = NULL;
	while(ps->head.next != &(ps->tail)){
		first = &(ps->head);
		mid = first->next;
		last = mid->next;
		if(mid != &(ps->tail)){
			first->next = last;
			free(mid);
			mid = NULL;
		}
	}
}

int queue_empty(const queue *ps)
{
	return ps->head.next == &(ps->tail);
}

int queue_size(const queue *ps)
{
	return ps->num;
}

int queue_push(queue *ps, int val)
{
	node *new = NULL;
	new = (node *)malloc(sizeof(node));
	if(!new)
		return 0;
	new->data = val;
	new->next = ps->head.next;
	ps->head.next = new;
	return 1;
}

int queue_pop(queue *ps, int *val)
{
	node *tmp = NULL;
	node *first = NULL, *mid = NULL, *last = NULL;
	if(ps->head.next == &(ps->tail))
		return 0;

	for(tmp = &(ps->head); tmp != &(ps->tail); tmp = tmp->next){
		first = tmp;
		mid = first->next;
		last = mid->next;
		if(last == &(ps->tail)){
			*val = mid->data;
			first->next = last;
			free(mid);
			mid = NULL;
			return 1;
		}
	}
}

int queue_front(const queue *ps, int *val)
{
	node *tmp = NULL;
	if(ps->head.next == &(ps->tail))
		return 0;
	tmp = ps->head.next;
	while(tmp->next != &(ps->tail)){
		tmp = tmp->next;
	}
	*val = tmp->data;
	return 1;
}

int main()
{
	int val = 0, ret = 0;
	queue sk = {0};
	queue_init(&sk);
	while(1){
		printf("input a number:");
		scanf("%d", &val);
		if(val < 0)
			break;
		ret = queue_push(&sk, val);
		if(!ret)
			break;
	}
	while(1){
		ret = queue_pop(&sk, &val);
		if(!ret)
			break;
		printf("%d ", val);
	}
	printf("\n");
	queue_delete(&sk);
	return 0;
}