使用数组的循环队列操作

Question

Code shows basic operations on Circular Queue.

#define maxsize 10
typedef struct queue
{
    int data[maxsize];
    int f,r;
}myQueue;
myQueue q;  

void init(myQueue *q);
int full(myQueue *q);
int empty(myQueue *q);
void enqueue(myQueue *q,int num);
void dequeue(myQueue *q);
void print(myQueue *q);

void main()
{
    init(&q);
    int op;
    do
    {
        printf("\nCircular queue operations: Press:\n");
        printf("1 for enqueue\n");
        printf("2 for dequeue\n");
        printf("3 to print Circular Queue\n");

        int num,choice;
        printf("\nEnter choice:\n");
        scanf("%d",&choice);
        switch(choice)
        {
             case 1: printf("Enter number to insert :\n");
                     scanf("%d",&num);
                     if(full(&q))
                     {
                         printf("\nQueue is full\n");
                         exit(0);
                     }
                     enqueue(&q,num);
                     break;
             case 2: if(empty(&q))
                     {
                         printf("\nQueue is empty\n");
                         exit(0);
                     }
                     dequeue(&q);
                     break;
             case 3: printf("Printing current queue: \n");
                     print(&q);
                     break;
             default:break;
        }
        printf("Press 1 to continue or 0 to exit:\n");
        scanf("%d",&op);
    }
    while(op);
}

void init(myQueue *q)
{
    q->f=-1;
    q->r=-1;
}

int full(myQueue *q)
{
    if((q->r+1)%maxsize==q->f)
    {
        return 1;
    }
    else
        return 0;
}

int empty(myQueue *q)
{
    if(q->r==-1)
    {
        return 1;
    }
    else
        return 0;
}   

enqueue function is used to add the elements into queue.

void enqueue(myQueue *q,int num)
{
    if(empty(&q))
    {
        q->f=0;
        q->r=0;
    }
    else
    {
        q->r=(q->r+1)%maxsize;
    }
    q->data[q->r]=num;
    printf("\n%d is enqueued\n",q->data[q->r]);
}

Dequeue function is used to delete elements from the stack.

void dequeue(myQueue *q)
{
    int del_num;
    del_num=q->data[q->f];
    if(q->f==q->r)
    {
        init(&q);
    }
    else
    {  //To move front to the next position in the circular array.
        q->f=(q->f+1)%maxsize;
    }
    printf("\n%d is dequeued\n",del_num);
}

void print(myQueue *q)
{
    int i;
    for(i=q->f;i!=q->r;i=(i+1)%maxsize)
    {
        printf("%d\n",q->data[i]);
    }
    printf("%d\n",q->data[q->r]);
}
    

Issue: Circular queue is automatically enqueuing the 0 element in it initially.However, rest of the operations are working just fine.

I am not able to identify, why it is automatically inserting 0 in the circular queue, without me enqueuing it.

Answer 1

您的 print() 函数始终将 q->data[q->r] 打印为最后一个操作。当您的队列为空时，这毫无意义。也许你可以这样避免它:

void print(myQueue *q)
{
    if (empty(q))
      return;

    int i;
    for(i=q->f;i!=q->r;i=(i+1)%maxsize)
    {
        printf("%d\n",q->data[i]);
    }
    printf("%d\n",q->data[q->r]);
}

无论如何，您的代码还有很多问题，我怀疑它是否可以正确编译。举个例子，函数 enqueue() 接收一个 myQueue* 类型的参数。然后它提供了空函数及其地址，但这是错误的。您必须将指针本身传递给函数，因此使用 q 而不是 &q。同样的错误一次又一次地重复。