circular queue program

hi, I am doing a simple circular queue program. below is waht I did so far. I have some question about this program.

1. there is a compile error after I add disp() function (like the code below), can someone help me fix it?
2. what is  rewind(stdin) use for?
3. what is different between return 0 and return 1?

thanks in advance!!

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#include <stdio.h>

#define MaxSize 5     /* size queue size */
int queue[MaxSize];     /* */
int head=0,             /* head indicator */
    tail=0;             /* tail indicator */
int queuein(int);
int queueout(int *);

void main(void)
{
    int c,n;

    while (printf("]"),(c=getchar())!=EOF){
        rewind(stdin);
        if (c=='i' || c=='I'){
            printf("data--> ");
            scanf("%d",&n);rewind(stdin);
            if (queuein(n)==-1){
                printf("Full\n");
            }
        }
        if (c=='o' || c=='O'){
            if (queueout(&n)==-1)
                printf("Empty\n");
            else
                printf("queue data --> %d\n",n);
        }
               
        if (c=='L' || c=='l'){
             disp();
        }
       
       
    }
}

int queuein(int n)       /* insert to queue*/
{
    if ((tail+1)%MaxSize !=head){
        queue[tail]=n;
        tail++;
        tail=tail%MaxSize;
        return 0;
    }
    else
        return -1;       /* queue is full */
}


int queueout(int *n)     /* rmove data from queue */
{
    if (tail!=head){
        *n=queue[head];
        head++;
        head=head%MaxSize;
        return 0;
    }
    else
        return -1;       /* queue is empty */
}

void disp(void)        /* display content of queue*/
{
    int i;

    i=head;
    while (i!=tail){
        printf("%d\n",queue[i]);
        i++;
        i=i%MaxSize;
    }