Find average of all nodes in a linked list in c

C program for Find average of all nodes in a linked list. Here more information.

// Include header file
#include <stdio.h>
#include <stdlib.h>
/*
  C program for
  Find average of all nodes in a linked list
*/
// Linked list node
typedef struct LinkNode
{
	// Define useful field of LinkNode
	int data;
	struct LinkNode * next;
}LinkNode;

LinkNode * getLinkNode(int data)
{
	// Create dynamic memory of LinkNode
	LinkNode * ref = (LinkNode * ) malloc(sizeof(LinkNode));
	if (ref == NULL)
	{
		// Failed to create memory 
		return NULL;
	}
	ref->data = data;
	ref->next = NULL;
	return ref;
}
typedef struct SingleLL
{
	// Define useful field of SingleLL
	struct LinkNode * head;
	struct LinkNode * tail;
}SingleLL;

SingleLL * getSingleLL()
{
	// Create dynamic memory of SingleLL
	SingleLL * ref = (SingleLL * ) malloc(sizeof(SingleLL));
	if (ref == NULL)
	{
		// Failed to create memory 
		return NULL;
	}
	// Set initial value
	ref->head = NULL;
	ref->tail = NULL;
	return ref;
}
void insert(SingleLL * ref, int data)
{
	LinkNode * node = getLinkNode(data);
	if (ref->head == NULL)
	{
		// Add first node
		ref->head = node;
	}
	else
	{
		// Add node at the end position
		ref->tail->next = node;
	}
	// New last node
	ref->tail = node;
}
// Display linked list element
void display(SingleLL * ref)
{
	if (ref->head == NULL)
	{
		return;
	}
	LinkNode * temp = ref->head;
	// iterating linked list elements
	while (temp != NULL)
	{
		printf(" %d →", temp->data);
		// Visit to next node
		temp = temp->next;
	}
	printf(" NULL\n");
}
// Calculate average of linked list nodes
void findAverage(SingleLL * ref)
{
	if (ref->head == NULL)
	{
		printf("\nEmpty linked List");
	}
	else
	{
		printf(" Linked Linked ");
		display(ref);
		// Define useful resultant variable
		double sum = 0;
		int size = 0;
		// Get first node of linked list
		LinkNode * auxiliary = ref->head;
		// iterating linked list elements
		while (auxiliary != NULL)
		{
			// Node counter
			size++;
			// Calculate the sum of node value
			sum += auxiliary->data;
			// Visit to next node
			auxiliary = auxiliary->next;
		}
		// Display result
		if (sum != 0)
		{
			printf(" Node Average : %0.2f", (sum / size));
		}
		else
		{
			printf(" Node Average : 0");
		}
	}
}
int main()
{
	SingleLL * sll = getSingleLL();
	// Add linked list node
	// 2 → 9 → 1 → 5 → 5 → 4 → 3 → 7 → NULL
	insert(sll, 2);
	insert(sll, 9);
	insert(sll, 1);
	insert(sll, 5);
	insert(sll, 5);
	insert(sll, 4);
	insert(sll, 3);
	insert(sll, 7);
	// Test
	findAverage(sll);
}

Output

 Linked Linked  2 → 9 → 1 → 5 → 5 → 4 → 3 → 7 → NULL
 Node Average : 4.50