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

typedef int Item;

typedef struct node {
    Item data;
    struct node *next;
} QueueNode;

// by putting head inside struct we get single pointer to hodl that does not change when top changes 
typedef struct {
    QueueNode* head;
    QueueNode* tail;
} QueueType;;

QueueType* createQueue()
{
    QueueType* s = malloc(sizeof(QueueType));
    return s;
}

void enqueue(QueueType* q, Item i)
{
    QueueNode* newNode = malloc(sizeof(QueueNode));
    newNode->data = i;
    if(q->tail==NULL)
    {
	q->head=newNode;
	q->tail=newNode;
    }
    else
    {
	q->tail->next=newNode;
	q->tail=newNode;
    }
}

void showQ(QueueType* q)
{
    QueueNode* qq=q->head;
    while(qq!=NULL)
    {
	printf("%d\n", qq->data);
	qq=qq->next;
    }
}
    

Item dequeue(QueueType* q)
{
    QueueNode* oldTop;
    if (q->head==NULL)
    {
	Item i;
	return i;
    }
    oldTop = q->head;
    q->head = oldTop->next;;
    Item d = oldTop->data;
    free(oldTop);
    return d;
}

int main(void)
{
    QueueType * s1;
    s1 = createQueue();
    enqueue(s1, 5);
    enqueue(s1, 10);
    enqueue(s1, 20);
    enqueue(s1, 40);
    enqueue(s1, 80);
    enqueue(s1, 160);
    showQ(s1);
    printf("%d\n", dequeue(s1));
    printf("%d\n", dequeue(s1));
}