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

struct fifo_node
 {
 int data;
 struct fifo_node *next;
 };

 struct fifo_pointers
 {
 struct fifo_node *head, *tail;
 } fifo;


void enqueue(struct fifo_pointers *fifo, int data)
 {
 struct fifo_node *new_node =
 (struct fifo_node *)malloc(sizeof(struct fifo_node));
 if(new_node) {
 new_node->data = data;
 new_node->next = NULL;
 if(fifo->head==NULL) fifo->head = fifo->tail = new_node;
 else {
 fifo->tail->next=new_node;
 fifo->tail=new_node;
 }
 } else
 fprintf(stderr,"Nowy element nie został utworzony!\n");
 }
int dequeue(struct fifo_pointers *fifo)
 {
 if(fifo->head) {
 struct fifo_node *tmp = fifo->head->next;
 int data = fifo->head->data;
 free(fifo->head);
 fifo->head=tmp;
 if(tmp==NULL)
 fifo->tail = NULL;
 return data;
 }
 return -1;
 }



 void print_queue_req(struct fifo_pointers tmp)
{
if(tmp.head != NULL) return 0;
 printf("%d ",tmp.head->data);
 fifo.head = tmp.head->next;

 print_queue_req(tmp);

 }


int main(void)
 {
 int i;
 for(i=0;i<20;i++)
 enqueue(&fifo,i);

 print_queue_req(fifo);

 while(fifo.head)
printf("%d ",dequeue(&fifo));
puts("");
 return 0;
 }