Arrange consonants and vowels nodes in a linked list

// C Program 
// Arrange consonants and vowels nodes in a linked list
#include <stdio.h>

#include <stdlib.h> //for malloc function

// Linked List LinkNode
struct LinkNode
{
    char data;
    struct LinkNode *next;
};
// Singly linked list 
struct SingleLL
{
    struct LinkNode *head;
    struct LinkNode *tail;
};
// Returns the new linked list
struct SingleLL *newLinkedList()
{
    // Create memory of head and tail Nodes
    struct SingleLL *sll = (struct SingleLL *) malloc(sizeof(struct SingleLL));
    if (sll == NULL)
    {
        printf("Memory overflow\n");
    }
    else
    {
        sll->head = NULL;
        sll->tail = NULL;
    }
    return sll;
}

// Add new Node at end of linked list 
void appendNode(struct SingleLL *sll,struct LinkNode *node )
{
    if (sll->head == NULL)
    {
        sll->head = node;
    }
    else
    {
        // Append the node at last position
        sll->tail->next = node;
    }
    sll->tail = node;
}


// Handles the request of adding new node in linked list
void addNode(struct SingleLL *sll, char data)
{
    // Create dynamic node
    struct LinkNode *node = (struct LinkNode *) malloc(sizeof(struct LinkNode));
    if (node == NULL)
    {
        printf("Memory overflow to Create LinkNode\n");
        return;
    }
    else
    {
        // Set initial node value
        node->data = data;
        node->next = NULL;
    }    
    appendNode(sll,node);
}


// Display linked list element
void display(struct SingleLL *sll)
{
    if (sll->head == NULL)
    {
        printf("\n Empty linked list\n");
        return;
    }
    struct LinkNode *temp = sll->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;
}
//  Arrange the nodes in front position of vowels and end with consonants
void arrangeNodes(struct SingleLL *sll)
{
    if (sll->head == NULL)
    {
        printf("\n Empty linked list\n");
        return;
    }
    // Define some auxiliary variable
    struct SingleLL *vowel      =  newLinkedList();
    struct SingleLL *consonant  =  newLinkedList();

    struct LinkNode*auxiliary   = sll->head;
    struct LinkNode*ordinary   = sll->head;

    // iterate linked list nodes
    while(auxiliary != NULL )
    {

        ordinary = auxiliary;

        auxiliary = auxiliary->next;

        if(isVowels(ordinary->data)== 1 )
        {
            // Add node into volwel list
            appendNode(vowel,ordinary);
        }
        else
        {
            appendNode(consonant,ordinary);
        }

        ordinary->next = NULL;
    }
    if(vowel->head != NULL)
    {
        // Set new head node of resultant linked list
        sll->head = vowel->head;

        // Connect vowel and consonant linked list
        vowel->tail->next = consonant->head;
        
        if(consonant->tail != NULL)
        {
            // When consonant node exists
            // Set new tail node of resultant linked list 
            sll->tail = consonant->tail;
        }
        else
        {
            // When consonant nodes not exists
            sll->tail = vowel->tail;
        }
    }
    else
    {
        // When vowels not exist
        sll->head = consonant->head;
        sll->tail - consonant->tail;
    }
}
int main()
{
    // Define linked list
    struct SingleLL *sll = newLinkedList();


    // Constructed linked list
    addNode(sll, 'R');
    addNode(sll, 'E');
    addNode(sll, 'G');
    addNode(sll, 'U');
    addNode(sll, 'L');
    addNode(sll, 'A');
    addNode(sll, 'T');
    addNode(sll, 'I');
    addNode(sll, 'O');
    addNode(sll, 'N');
    printf(" Before Arrange \n");
    // R → E → G → U → L → A → T → I → O → N → NULL
    display(sll);

    arrangeNodes(sll);

    printf(" After Arrange \n");
    // E → U → A → I → O → R → G → L → T → N → NULL
    display(sll);
 
    return 0;
}

Output

 Before Arrange
 R → E → G → U → L → A → T → I → O → N → NULL
 After Arrange
 E → U → A → I → O → R → G → L → T → N → NULL