queue implementation in c using array

 // queue.cpp : Defines the entry point for the console application.  
 //  
 #include "stdafx.h"  
 #include <stdio.h>  
 #include <stdlib.h>  
 struct queue  
 {  
 int front;  
 int rear;  
 int a[5];  
 int capacity;  
 };  
 void enqueue(struct queue *q, int data)  
 {  
      if((q->front == ((q->rear+1)%q->capacity)))  
      {       
           printf("Queue full");  
           return ;  
      }  
      if(q->front == -1)  
      q->front=0;  
      q->rear = (++q->rear)%q->capacity;  
      q->a[q->rear]=data;  
      printf("front %d rear %d\n",q->front,q->rear);  
 }  
 void dequeue(struct queue *q)  
 {  
      if((q->front == -1) && (q->rear == -1))  
      {  
           printf("\n queue empty");  
           return;  
      }  
      if(q->front == q->rear)  
      {  
           q->front = -1;  
           q->rear = -1;  
           return;  
      }  
      q->front = (++q->front)%q->capacity;  
 }  
 void display(struct queue q)  
 {  
      if((q.front == -1) && (q.rear == -1))  
      {  
           printf("\n queue empty");  
           return;  
      }  
      for(int i=q.front;;i++)  
      {  
           i = i%(q.capacity);  
           printf("-%d-",q.a[i]);  
           if(i==q.rear)  
                break;  
      }  
 }  
 int main(int argc, char* argv[])  
 {  
      int ch=0, data = 0;  
      struct queue q;  
      q.capacity = 5;  
      q.front = -1;  
      q.rear = -1;  
      printf("1.enqueue\n2.dequeue\n3.display\n4.exit");  
      while(1)  
      {  
      printf("\nEnter the option!\n");  
      scanf("%d",&ch);  
      switch(ch)  
      {  
      case 1: printf("Enter data:");  
                scanf("%d",&data);  
                enqueue(&q,data);  
                break;  
      case 2: dequeue(&q);  
                break;  
      case 3: display(q);  
                break;  
      case 4: exit(0);  
      }  
      }       
      return 0;  
 }