使用数组队列 [英] Queue using Arrays

问题描述

下面是我的实现使用数组一个简单的队列中。

Below is my implementation of a simple queue using arrays.

#include<stdio.h>
#include<stdlib.h>
#define QSIZE 5 //Limit size of queue to just 5 enteries

/*Beginning of prototype for queue functions: Insert, retrieve and display*/
void qdisp(); //Display to queue array contents
void qinsert(); //Insert a element into rear of queue
int qdelete(); //Remove an element from front of queue
/*End of prototyping*/

// Variables
int fe=0,re=0,q[QSIZE],item; //fe(front entry), re(rear entry), q[](queue array), item(element to i/p or delete)

void main()
{
  int choice;
  while(1)
  {
    printf("1.Insert element\n2.Remove element\n3.Display element(s)\n4.Exit program\nEnter number for appropriate choice:  ");
    scanf("%d",&choice);
    switch(choice)
    {
      case 1:   printf("Enter value of element: ");
            scanf("%d",&item);
            qinsert();
            break;
      case 2:   item=qdelete();
            printf("Removed \'%d\' from the queue\n",item);
            break;
      case 3:   qdisp();
            break;
      case 4:   exit(0);

      /*case default : printf("Wrong choice i/p!");
              break;*/
    }
  }
}
//End of main, beginning for function definitons

void qinsert()
{
  if(re==QSIZE-1)
  {
    printf("Queue Overflow\n");
    exit(0);
  }
  q[re]=item;
  re++;
}

int qdelete()
{
  if(fe>re)
  {
    printf("Queue is empty!\n");
    exit(0);
  }

  item=q[fe];
  fe++;
  return item;
}

void qdisp()
{
  int i; //i is loop counter variable
  if(fe>re)
  {
    printf("Queue is empty!\n");
    exit(0);
  }
  printf("Queue items are: \n");
  for(i=fe;i<=re;i++)
    printf("%d\n",q[i]);
}

我在队列中，因为最初使用初始前后条目0则先成为最后一个条目以及任何条目。但是我的老师说我应该保持后条目-1，并同时将元素插入队列中，先增加后进入指数，然后加入反对的第一个再加入我的递增code。我看着它，并在网上和到现在为止我没有找到我怎么错了。

I have used initial front and rear entry as 0 since initially in a queue any entry that goes first becomes the last entry as well. However my teacher says I should keep the rear entry as '-1' and while inserting an element into queue, first increment the rear entry index and then add opposing my code of first adding then incrementing. I looked into it and online and till now I don't find how I'm wrong.

我提供的信息，如果我错了，还是我的老师是？

Provide me information if I'm wrong or my teacher is?

推荐答案

这两个pre-递增和递增后可以在队列中使用。然而什么改变是全空的条件。随着pre-增量全部条件是 QSIZE-1 ，具有后递增，充分条件是 QSIZE 。随着pre-增量空的条件是 FE ==再，后增 FE＆GT;再。

Both pre-incrementing and post-incrementing can be used in a queue. What changes however is the full and empty conditions. With pre-increment the full condition is QSIZE-1, with post-incrementing the full condition is QSIZE. With pre-increment the empty condition is fe==re, with post-increment fe>re.

使用pre-增量可以保存删除一个临时变量。请注意如何你必须保存当前的元素融入项目，然后递增指标，然后返回项目。

Using pre-increment can save a temporary variable in delete. Notice how you must save the current element into item, then increment the index, then return item.

item=q[fe];
fe++;
return item;

您可以通过增加指数与项目变量做掉，然后的返回的元素。

You can do away with the item variable by incrementing the index, then returning the element.

fe++;
return q[fe];

记住，如果你pre-增量插入，你需要pre-增量删除。

Just remember, if you pre-increment to insert, you need to pre-increment to delete.

好吧，考虑这一点。会发生什么 FE 和重新都是 QSIZE-1 ？队列是空的，但你的code会间preT它作为完整的（因为重新== QSIZE-1 ）。

Ok, consider this. What happens fe and re are both QSIZE-1? The queue is empty but your code will interpret it as full (because re==QSIZE-1).

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