Find all unique elements in linked list

// C Program
// Find all unique elements in linked list

#include <stdio.h>
 //For malloc function
#include <stdlib.h>

//Linked List Node
struct Node
{
	int data;
	struct Node *next;
};
//Create a node of linked list
struct Node *create_node(int data)
{
	//Create dynamic node
	struct Node *node = (struct Node *) malloc(sizeof(struct Node));
	if (node == NULL)
	{
		printf("Memory overflow\n");
	}
	else
	{
		//Set initial node value
		node->data = data;
		node->next = NULL;
	}
	return node;
}
//Add new node at end of linked list 
void insert(struct Node **head, int data)
{
	struct Node *node = create_node(data);
	if ( *head == NULL)
	{
		*head = node;
	}
	else
	{
		struct Node *temp = *head;
		//Find last node
		while (temp->next != NULL)
		{
			temp = temp->next;
		}
		//Add node at last possition
		temp->next = node;
	}
}
//Display linked list element
void display(struct Node *head)
{
	if (head == NULL)
	{
		printf("\nEmpty linked list\n");
		return;
	}
	struct Node *temp = head;
	printf("\n Linked List : ");
	//iterating linked list elements
	while (temp != NULL)
	{
		printf("  %d", temp->data);
		//visit to next node
		temp = temp->next;
	}
	printf("\n");
}
//This are find out all unique elements in given array
void unique_elements(struct Node *head)
{
	//Define some auxiliary variables
	struct Node *outer = head;
	struct Node *inner = NULL;
	//Resultant variables
	int status = 0;
	int counter = 1;
	printf(" Unique Elements : ");
	//Below process takes O(n*n) time
	//iterating linked list elements
	while (outer != NULL)
	{
		inner = head;
		//iterating linked list elements
		while (inner != NULL && counter <= 1)
		{
			if (inner != outer && inner->data == outer->data)
			{
				//When element are duplicate
				counter++;
			}
			//visit to next node
			inner = inner->next;
		}
		if (counter == 1)
		{
			status = 1;
			printf("  %d", outer->data);
		}
		//reset the counter value
		counter = 1;
		//visit to next node
		outer = outer->next;
	}
	if (status == 0)
	{
		printf(" None ");
	}
	printf("\n");
}
int main()
{
	struct Node *head = NULL;
	//Create linked list
	insert( &head, 2);
	insert( &head, 4);
	insert( &head, 7);
	insert( &head, 2);
	insert( &head, 5);
	insert( &head, 7);
	insert( &head, 1);
	insert( &head, 3);
	insert( &head, 1);
	insert( &head, 2);
	//Display of linked list nodes
	display(head);
	unique_elements(head);
	return 0;
}

Output

 Linked List :   2  4  7  2  5  7  1  3  1  2
 Unique Elements :   4  5  3