Remove duplicates from unsorted linked list in c

C program for Remove duplicates from unsorted linked list. Here problem description and explanation.

/*
    C program for
    Delete duplicate nodes in unsorted linked list
*/
#include <stdio.h>
#include <stdlib.h>

// Linked List LinkNode
struct LinkNode
{
    int data;
    struct LinkNode *next;
};
// Singly linked list 
struct SingleLL
{
    struct LinkNode *head;
    struct LinkNode *tail;
};
// Returns the new linked list
struct SingleLL *newLinkedList()
{
    // Create new linked list
    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;
}
// Handles the request of adding new node at end of linked list
void addNode(struct SingleLL *sll, int 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;
    }
    if (sll->head == NULL)
    {
        sll->head = node;
    }
    else
    {
        sll->tail->next = node;
    }
    sll->tail = node;
}
// Display linked list element
void display(struct LinkNode *node)
{
    if (node == NULL)
    {
        return;
    }
    struct LinkNode *temp = node;
    // iterating linked list elements
    while (temp != NULL)
    {
        printf(" %d →", temp->data);
        // Visit to next node
        temp = temp->next;
    }
    printf(" NULL\n");
}
void removeNode(struct SingleLL *sll)
{
    if (sll->head == NULL)
    {
        // When linked list empty
        return;
    }
    else
    {
        // Auxiliary variable
        struct LinkNode *temp = sll->head;
        struct LinkNode *hold = NULL;
        struct LinkNode *initial = NULL;
        struct LinkNode *current = NULL;
        // Outer loop
        while (temp != NULL)
        {
            current = temp;
            sll->tail = current;
            initial = current->next;
            // Inner loop
            // Remove all node which value is similar to temp node
            while (initial != NULL)
            {
                if (temp->data == initial->data)
                {
                    // Get remove node
                    hold = initial;
                }
                else
                {
                    current = initial;
                }
                // Visit to next node
                initial = initial->next;
                if (hold != NULL)
                {
                    // remove node
                    current->next = initial;
                    free(hold);
                    hold = NULL;
                }
            }
            // Visit to next node
            temp = temp->next;
        }
    }
}
int main(int argc, char
    const *argv[])
{
    struct SingleLL *sll = newLinkedList();
    // Sorted Linked list node
    addNode(sll, 1);
    addNode(sll, 2);
    addNode(sll, 9);
    addNode(sll, 4);
    addNode(sll, 9);
    addNode(sll, 3);
    addNode(sll, 1);
    addNode(sll, 7);
    addNode(sll, 2);
    addNode(sll, 1);
    printf(" Before Delete \n");
    display(sll->head);
    removeNode(sll);
    printf(" After Delete \n");
    display(sll->head);
    return 0;
}

Output

 Before Delete
 1 → 2 → 9 → 4 → 9 → 3 → 1 → 7 → 2 → 1 → NULL
 After Delete
 1 → 2 → 9 → 4 → 3 → 7 → NULL