text: #include <stdio.h>
  #include <stdbool.h>
  #include "queue.h"
  
  int main(void)
  {
      Queue q;
  
      init_queue(&q);
      enqueue(&q, 520);
      enqueue(&q, 10);
      enqueue(&q, 37);
      enqueue(&q, 100);
  
      printf("Front number in the queue: %d\n", front(&q));
      printf("Back number in the queue: %d\n", back(&q));
      printf("Items: ");
      traverse(&q);
      putchar('\n');
  
      dequeue(&q);
      dequeue(&q);
      dequeue(&q);
      dequeue(&q);
      dequeue(&q); // It should print error message.
      traverse(&q); // Also.
  
      puts("Enqueue 1 in the queue.");
      enqueue(&q, 1);
      printf("Items: ");
      traverse(&q);
  
      free_all(&q);
      return 0;
  }
  
  /*
  Input: 
  No input
  
  Output:
  Front number in the queue: 520
  Back number in the queue: 100
  Items: 520 10 37 100
  
  ERROR: The queue is empty.
  ERROR: The queue is empty.
  Enqueue 1 in the stack.
  Items: 1
  */