第 17 章 高级数据表示（测试队列）

/*------------------------
    queue.h -- Queue接口
------------------------*/

#ifndef QUEUE_H
#define QUEUE_H

#define MAXQUEUE 10

typedef int Item;

typedef struct node
{
    Item item;
    struct node *next;
} Node;

typedef struct queue
{
    Node *front;    //指向队列首项的指针
    Node *rear;        //指向队列尾项的指针
    int items;        //队列中的项数
} Queue;

//初始化队列为空
void InitializeQueue(Queue *pq);

//检查队列是否已满，已满返回true,否则返回false
bool QueueIsFull(const Queue *pq);

//检查队列是否为空，为空返回true,否则返回false
bool QueueIsEmpty(const Queue *pq);

//确定队列的项数
int QueueItemCount(const Queue *pq);

//在队列末尾添加项：item是被添加在队列末尾的项
bool EnQueue(Item item, Queue *pq);

//在队列开头删除项：队列不为空，队列首位item将被拷贝到*pitem中
bool DeQueue(Item *pitem, Queue *pq);

//清空队列
void EmptyTheQueue(Queue *pq);

#endif

/*----------------------------
    queue.c -- Queue 实现
----------------------------*/

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

static void CopyToNode(const Item *pi, Node *pn)
{
    pn->item = *pi;
}

static void CopyToItem(const Node *pn, Item *pi)
{
    *pi = pn->item;
}

void InitializeQueue(Queue *pq)
{
    pq->front = pq->rear = NULL;
    pq->items = 0;
}

bool QueueIsFull(const Queue *pq)
{
    return pq->items == MAXQUEUE;
}

bool QueueIsEmpty(const Queue *pq)
{
    return pq->items == 0;
}

int QueueItemCount(const Queue *pq)
{
    return pq->items;
}

bool EnQueue(Item item, Queue *pq)
{
    if (QueueIsFull(pq)) return false;

    Node *pnew = (Node*)malloc(sizeof(Node));
    if (pnew == NULL)
    {
        fprintf(stderr, "Unable to allocate memory!
");
        exit(EXIT_FAILURE);
    }

    CopyToNode(&item, pnew);
    pnew->next = NULL;

    if (QueueIsEmpty(pq))
        pq->front = pnew;                //新添项位于队列头端
    else
        pq->rear->next = pnew;          //新添项链接到队列尾端

    pq->rear = pnew;                    //记录队列尾端的位置
    ++(pq->items);                      //队列项数加1

    return true;
}

bool DeQueue(Item *pitem, Queue *pq)
{
    if (QueueIsEmpty(pq)) return false;

    CopyToItem(pq->front, pitem);

    Node *pt = pq->front;
    pq->front = pt->next;
    free(pt);
    --(pq->items);

    if (QueueIsEmpty(pq)) pq->rear = NULL;

    return true;
}

void EmptyTheQueue(Queue *pq)
{
    Item dummy;
    while (!QueueIsEmpty(pq)) DeQueue(&dummy, pq);
}

/*---------------------------------------
    use_q.c -- 驱动程序测试 Queue 接口
---------------------------------------*/

#include <stdio.h>
#include "queue.h"

int main()
{
    Queue line;
    Item temp;
    char ch;

    InitializeQueue(&line);

    puts("Testing the Queue interface. Type "a" to add a value, ");
    puts("type "d" to delete a value, and type "q" to quit.");

    while ((ch = getchar()) != 'q')
    {
        if (ch != 'a' && ch != 'd') continue;    //忽略其他输出

        if (ch == 'a')        //add
        {
            printf("Integer to add: ");
            scanf("%d", &temp);
            
            if (!QueueIsFull(&line))
            {
                printf("Putting %d into queue
", temp);
                EnQueue(temp, &line);
            }
            else
                puts("Queue is full!");
        }
        else                //delete
        {
            if (QueueIsEmpty(&line))
                puts("Nothing to delete!");
            else
            {
                DeQueue(&temp, &line);
                printf("Removing %d from queue
", temp);
            }
        }

        printf("%d items in queue
", QueueItemCount(&line));
        puts("Type "a" to add, "d" to delete, "q" to quit;");
    }

    EmptyTheQueue(&line);
    puts("Bye!");

    return 0;
}