Move vowels node at the beginning of linked list in c

C program for Move vowels node at the beginning of linked list. Here more information.

// Include header file
#include <stdio.h>
#include <stdlib.h>
/*
  C program for
  Shift the vowels node at beginning of linked list
*/
// Linked list node
typedef struct LinkNode
{
	// Define useful field of LinkNode
	char data;
	struct LinkNode * next;
}LinkNode;

LinkNode * getLinkNode(char 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;
	}
	ref->head = NULL;
	ref->tail = NULL;
	return ref;
}

// Add new node at end of linked list 
void addNode(SingleLL * ref, char data)
{
	LinkNode * node = getLinkNode(data);
	if (ref->head == NULL)
	{
		ref->head = node;
	}
	else
	{
		// Append the node at last position
		ref->tail->next = node;
	}
	ref->tail = node;
}
// Display linked list element
void display(SingleLL * ref)
{
	if (ref->head == NULL)
	{
		printf("\n Empty linked list");
		return;
	}
	LinkNode * temp = ref->head;
	// iterating linked list elements
	while (temp != NULL)
	{
		printf(" %c →", temp->data);
		// Visit to next node
		temp = temp->next;
	}
	printf(" NULL\n");
}
// Determine that given value is an vowel or not
int isVowels(char value)
{
	if (value == 'a' || value == 'e' || 
        value == 'i' || value == 'o' || 
        value == 'u' || value == 'A' || 
        value == 'E' || value == 'I' || 
        value == 'O' || value == 'U')
	{
		return 1;
	}
	return 0;
}
// Move the vowels value at beginning position
void shiftVowels(SingleLL * ref)
{
	if (ref->head == NULL)
	{
		printf("\n Empty linked list\n");
		return;
	}
	// Define some auxiliary variable
	LinkNode * node = ref->head;
	LinkNode * back = NULL;
	// iterate linked list nodes
	// And shift vowels at front of linked list
	while (node != NULL)
	{
		if (isVowels(node->data) == 1 && back != NULL)
		{
			// Enter here when
			// Node is contain vowel and 
			// its previous (any) node is not form of vowel
			if (node == ref->tail)
			{
				// When is last node
				// Set new last node
				ref->tail = back;
			}
			// Connect previous node to next node
			back->next = node->next;
			// Connect vowel node to first node
			node->next = ref->head;
			// Set new head
			ref->head = node;
			// Get back node
			node = back;
		}
		else
		{
			back = node;
		}
		// Visit to next node
		node = node->next;
	}
}
int main()
{
	SingleLL * sll = getSingleLL();
	// Constructed linked list
	addNode(sll, 'E');
	addNode(sll, 'D');
	addNode(sll, 'U');
	addNode(sll, 'C');
	addNode(sll, 'A');
	addNode(sll, 'T');
	addNode(sll, 'I');
	addNode(sll, 'O');
	addNode(sll, 'N');
	printf(" Before move vowels\n");
	// E → D → U → C → A → T → I → O → N → NULL
	display(sll);
	shiftVowels(sll);
	printf(" After move vowels\n");
	// O → I → A → U → E → D → C → T → N → NULL
	display(sll);
}

Output

 Before move vowels
 E → D → U → C → A → T → I → O → N → NULL
 After move vowels
 O → I → A → U → E → D → C → T → N → NULL