$ cat new.c
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define pp(x)      printf("%s = %p\n", #x, x);
#define pi(x)      printf("%s = %d\n", #x, x);
#define pc(x)      printf("%s = %c\n", #x, x);

// A C program to demonstrate linked list based implementation of queue 
// A linked list (LL) node to store a queue entry
int index_start = -1;
int ref_start = 0;
struct QNode
{
	int index;
	int ref;
	struct QNode *next;
};

// The queue, front stores the front node of LL and rear stores ths
// last node of LL
struct Queue
{
	struct QNode *front, *rear;
};

// A utility function to create a new linked list node.
struct QNode* newNode(void)
{
	struct QNode *temp = (struct QNode*)malloc(sizeof(struct QNode));
	temp->index = index_start++;
	temp->ref = ref_start++;
	temp->next = NULL;
	return temp;
}

// A utility function to create an empty queue
struct Queue *createQueue()
{
	struct Queue *q = (struct Queue*)malloc(sizeof(struct Queue));
	q->front = q->rear = NULL;
	return q;
}

void store_asm(struct Queue *q)
{
	// Create a new LL node
	struct QNode *temp = newNode();

	// If queue is empty, then new node is front and rear both
	if (q->rear == NULL)
	{
	q->front = q->rear = temp;
	return;
	}

	// Add the new node at the end of queue and change rear
	q->rear->next = temp;
	q->rear = temp;
}

struct QNode * load_asm(struct Queue **q)
{
	// If queue is empty, return NULL.
	if ((q) == NULL) return NULL;
	if ((*q) == NULL) return NULL;
	if ((*q)->front == NULL)
	return NULL;

	// Store previous front and move front one node ahead
	struct QNode *temp = (*q)->front;
	(*q)->front = (*q)->front->next;

	// If front becomes NULL, then change rear also as NULL
	if ((*q)->front == NULL)
	(*q)->rear = NULL;
	return temp;
}

int queue_add(struct Queue **q) {
	if (!(*q)) (*q) = createQueue();
	store_asm((*q));
	return 0;
}

struct Queue * list = NULL;
int main(void) {
	index_start = 0;
	ref_start = 1;
	queue_add(&list);
	queue_add(&list);
	queue_add(&list);
	struct QNode * p = list->front;
	while(p) {
		printf("%d -> %d\n", p->index, p->ref);
		p = p->next;
	}
	puts("NULL");
	return 0;
}

$ gcc new.c -o new


$ ./new
0 -> 1
1 -> 2
2 -> 3
NULL