链式队列的实现

queue.h

#ifndef QUEUE_H
#define QUEUE_H

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

//node
typedef struct QueueNode
{
    int data;
    struct QueueNode* next;
}NODE;

//queue
typedef struct
{
    NODE *front;
    NODE *rear;
}LinkQueue;

//初始化
void init(LinkQueue *q);
//创建队列
void create(LinkQueue *q);
//添加一个元素至队尾
void append(LinkQueue *q, int val);
//从队头删除一个元素
void serve(LinkQueue *q, int *val);
//获取队首的元素值
void top(LinkQueue *q, int *val);

//判断队列是否为空
int isEmpty(LinkQueue *q);
//获取队列的长度
int length(LinkQueue *q);
//打印队列
void print(LinkQueue *q);
//清除队列
void clear(LinkQueue *q);


#endif

queue.c

#include "queue.h"

void init(LinkQueue *q)
{
    q->front = q->rear = (NODE*)malloc(sizeof(NODE));
    q->front->next = NULL;
}

void create(LinkQueue *q)
{
    init(q);
    int index;
    for(index = 0; index < 15; index++)
        append(q,rand() % 100);
}

void append(LinkQueue *q, int val)
{
    NODE *newNode = (NODE*)malloc(sizeof(NODE));
    newNode->data = val;
    if(newNode)
    {
        newNode->next = NULL;
        q->rear->next = newNode;
        q->rear = newNode;
    }
}

void serve(LinkQueue *q, int *val)
{
    if(q->front == q->rear)
    {
        printf("The queue is empty!
");
        return;
    }
    NODE *oldNode = q->front->next;
    *val = oldNode->data;
    //只有一个元素,队列置空
    if(q->front->next == q->rear)
        q->rear = q->front;
    q->front->next = oldNode->next;
    free(oldNode);
}

int isEmpty(LinkQueue *q)
{
    if(q->front == q->rear)
        return 1;
    return 0;
}

int length(LinkQueue *q)
{
    int len = 0;
    NODE *pcur = q->front;
    while(pcur != q->rear)
    {
        len++;
        pcur = pcur->next;
    }
    return len;
}

void clear(LinkQueue *q)
{
    NODE *ptem, *pcur;
    pcur = q->front->next;
    while(pcur)
    {
        ptem = pcur;
        pcur = pcur->next;
        free(ptem);
    }
    //删去头结点
    pcur = q->front;
    q->front = q->rear = NULL;
    free(pcur);
}

void print(LinkQueue *q)
{
    if(q->front == q->rear)
    {
        printf("The queue is empty!
");
        return;
    }
    NODE *pcur = q->front->next;
    while(pcur)
    {
        printf("->%2d",pcur->data);
        pcur = pcur->next;
    }
    printf("
");
}

void top(LinkQueue *q, int *val)
{
    if(q->front == q->rear)
    {
        printf("The queue si empty!
");
        return;
    }
    *val = q->front->next->data;
}

main.c

#include "queue.h"

int main()
{
    LinkQueue q;
    create(&q);

    int len = length(&q);
    int index, val;

    printf("依次出队:
");
    for(index = 0; index < len; index++)
    {
        serve(&q,&val);
        printf("->%2d",val);
    }
    printf("
");
    clear(&q);

    return 0;
}