/*
 * An example for queue implemented in fixed size array
 * usually called circular or ring buffer
 */

#include <stdio.h>
#include <stdlib.h>

#define SIZE 100

typedef struct {
  int data[SIZE];
  int head;
  int tail;
} Queue;

void enqueue(Queue* q, int d) {
  q->data[q->tail] = d;
  if(q->tail==SIZE-1) q->tail = 0;
  else q->tail = q->tail+1;
}

int dequeue(Queue* q) {
  int temp = q->data[q->head];
  if(q->head==SIZE-1) q->head = 0;
  else q->head = q->head+1;
  return temp;
}

void init(Queue* q) {
  Q->head = 0;
  q->tail = 0;
}

void print_queue(Queue* q) {
  if(q->tail==q->head) {
	  printf("empty queue.\n"); return;
  }
  if(q->tail>q->head) {
	int len = q->tail-q->head;
	while(len) {
	  printf("%d ", q->data[q->tail-len]);
	  len --;
	}
	printf("\n");
  }
  // what if q->tail < q->head? add your code below
 
}

int main() {

  Queue q;
  init(&q);
  print_queue(&q);
  enqueue(&q, 1);
  print_queue(&q);  
  enqueue(&q, 2);  
  print_queue(&q);
  
  return 0;
}