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

typedef struct Node node;
struct Node {
  int id;
  struct Node *next;
};

typedef struct Queue queue;
struct Queue {
  node *head;
  node *tail;
};

int peek(queue *q) { return q->head->id; }

void insert(queue *q, int id) {
  node *new = malloc(sizeof(node));
  new->id = id;
  new->next = NULL;

  if (q->tail)
    q->tail->next = new;
  else
    q->head = new;

  q->tail = new;
}

void delete (queue *q) {
  if (!q->head)
    return;

  node *next = q->head->next;

  free(q->head);

  q->head = next;

  if (!q->head)
    q->tail = NULL;
}

void display(queue *q) {
  node *cur = q->head;
  while (cur != NULL) {
    printf("%d ", cur->id);
    cur = cur->next;
  }
  printf("\n");
}

int main() {
  queue *q = malloc(sizeof(queue));
  insert(q, 56);
  insert(q, 3);
  insert(q, 99);
  delete(q);
  display(q);

  // free
  while (q->head != NULL)
    delete(q);
  free(q);
}