C环状队列

#include
#define maxsize 10

typedef struct
{
    int elem[maxsize];
    int front,rear;
}queue;

void init_queue(queue *cp)
{
    cp->front=0;
    cp->rear=0;
}

void en_queue(queue *cp,int x)
{

    if((cp->rear+1)%maxsize==cp->front)
        printf("The quequ is full!!");

    else
    {
        cp->rear=(cp->rear+1)%maxsize;
        cp->elem[cp->rear]=x;

    }
}

int dl_queue(queue *cp)
{

    if(cp->front==cp->rear)
        {printf("The queue is empty!!");
        return -1;
         }
    else
    {
        cp->front=(cp->front+1)%maxsize;
        return(cp->elem[cp->front]);

     }
}

void print(queue *cp)
{
    int i;
    for(i=cp->front+1;i<=cp->rear;i++)
    {
        printf("[%d]",cp->elem[i]);
    }
}

void main()
{
    int x,y;
    int select;
    queue *cp=NULL;

    init_queue(cp);

    do
    {
        printf("\n(1) Input a data");
        printf("\n(2) Output a  data");
        printf("\n(3) Exit");
        printf("\nPlease select one:");
        scanf("%d",&select);

        switch(select)
        {
            case 1:printf("\nPlease input the data:");
                   scanf("%d",&x);
                   en_queue(cp,x);
                   printf("\nThe queue is: ");
                   print(cp);
                   break;
            case 2:y=dl_queue(cp);
                   printf("\nThe queue is: ");
                   print(cp);
                   printf("\nThe putout data is %d",y);
                   break;
            case 3:break;
        }
    }
    while(select<3);
    getch();
}