链式队列的实现

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

typedef int ElemType;

typedef struct Node{
	ElemType data;
	struct Node *next;
}QueueNode;

typedef struct {
	QueueNode *front;
	QueueNode *rear;
}Queue;

void Init(Queue *q);
bool IsEmpty(Queue *q);
void Enter(Queue *q, ElemType e);
void Depart(Queue *q, ElemType *e);
void GetHeader(Queue *q, ElemType *e);
void Print(Queue *q);
void Clear(Queue *q);

void Init(Queue *q)
{
	q->front = q->rear = NULL;
}

bool IsEmpty(Queue *q)
{
	return (q->front == q->rear) ? true : false;
}

void Enter(Queue *q, ElemType e)
{
	QueueNode *node = (QueueNode *)malloc(sizeof(QueueNode));
	if (node)
	{
		if (NULL == q->front)
		{
			q->front = q->rear = node;
			node->data = e;
			node->next = NULL;
			return;
		}

		node->data = e;
		node->next = NULL;
		q->rear->next = node;
		q->rear = node;
	}
}

void Depart(Queue *q, ElemType *e)
{
	if (q->front == q->rear)
		return;

	QueueNode *temp = q->front;
	*e = temp->data;
	q->front = temp->next;
	free(temp);
}

void GetHeader(Queue *q, ElemType *e)
{
	if (!IsEmpty(q))
		*e = q->front->data;
}

void Print(Queue *q)
{
	QueueNode *p = q->front;
	while (p)
	{
		printf("%d ", p->data);
		p = p->next;
	}
	printf("\n");
}

void Clear(Queue *q)
{
	QueueNode *p = q->front;
	while (p)
	{
		QueueNode *temp = p;
		p = p->next;
		free(temp);
	}
	q->front = q->rear = NULL;
}

int main()
{
	Queue q;
	Init(&q);
	for(int i = 1; i <= 20; ++i)
		Enter(&q, i);
	Print(&q);

	ElemType e;
	Depart(&q, &e);
	printf("出队一次，出队元素为：%d\n", e);
	
	GetHeader(&q, &e);
	printf("此时队首元素为：%d\n", e);

	Clear(&q);
	printf("清空该队列，此时");

	if(IsEmpty(&q))
		printf("队列为空\n");
	else
		printf("队列不为空\n");

	return 0;
}