C Program for Circular Linked List Insertion in the middle

#include<stdio.h>
#include<stdlib.h>

struct Node
{
  int data;
  struct Node *next;
};

int size = 0;

void insert (struct Node **head, int data)
{

  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));
  newNode->data = data;

  // if its the first node being entered
  if (*head == NULL)
    {
      *head = newNode;
      (*head)->next = *head;
      size++;
      return;
    }

  // if LL already as >=1 node
  struct Node *curr = *head;

  // traverse till last node in LL
  while (curr->next != *head)
    {
      curr = curr->next;
    }
  curr->next = newNode;
  newNode->next = *head;
  *head = newNode;

  size++;
}

void insertMiddle (struct Node **head, int data)
{

  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));
  newNode->data = data;

  // if the LL was empty
  if (*head == NULL)
    {
      // use insert function to insert
      insert (head, data);
      return;
    }

  // otherwise
  struct Node *temp = *head;

  // find correct insertion position for middle
  int mid = (size % 2 == 0) ? (size / 2) : (size + 1) / 2;

  // Unique case when there is only one node in CLL
  // we will be inserting at the last, 
  // inserting 2nd node at the last
  // Example size = 1 will result in mid = 1 so entering after 1st node
  // where size itself is 1 so entering last node
  if (mid == size)
    {
      newNode->next = *head;
      (*head)->next = newNode;
      size++;
      return;
    }
  // traverse to current mid position
  while (--mid)
    {
      temp = temp->next;
    }

  newNode->next = temp->next;
  temp->next = newNode;
  size++;
}

void display (struct Node *head)
{
  // if there are no node in LL
  if (head == NULL)
    return;

  struct Node *temp = head;

  //need to take care of circular structure of LL
  do
    {
      printf ("%d ", temp->data);
      temp = temp->next;

    }
  while (temp != head);
  printf ("\n");
}

int main ()
{
  struct Node *head = NULL;

  insert (&head, 25);
  insert (&head, 5);

  display (head);

  insertMiddle (&head, 10);
  display (head);

  insertMiddle (&head, 20);
  display (head);

  insertMiddle (&head, 15);
  display (head);

  return 0;
}

Output

5 25 
5 10 25 
5 10 20 25 
5 10 15 20 25

#include<stdio.h>
#include<stdlib.h>

struct Node
{
  int data;
  struct Node *next;
};

int calcSize (struct Node *head);

void insertStart (struct Node **head, int data)
{
  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));
  newNode->data = data;

  // if its the first node being entered
  if (*head == NULL)
    {
      *head = newNode;
      (*head)->next = *head;
      return;
    }

  // if LL already as >=1 node
  struct Node *curr = *head;

  // traverse till last node in LL
  while (curr->next != *head)
    {
      curr = curr->next;
    }
  // assign LL's last node's next as this new node
  curr->next = newNode;

  // assign newNode's next as current head
  newNode->next = *head;

  // change head to this new node
  *head = newNode;
}

void insertMiddle (struct Node **head, int data)
{
  int size = calcSize (*head);

  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));
  newNode->data = data;

  // if the LL was empty
  if (*head == NULL)
    {
      // use insert function to insert
      insertStart (head, data);
      return;
    }

  // otherwise
  struct Node *temp = *head;

  // find correct insertion position for middle
  int mid = (size % 2 == 0) ? (size / 2) : (size + 1) / 2;

  // Unique case when there is only one node in CLL
  // we will be inserting at the last, 
  // inserting 2nd node at the last
  // Example size = 1 will result in mid = 1 so entering after 1st node
  // where size itself is 1 so entering last node
  if (mid == size)
    {
      newNode->next = *head;
      (*head)->next = newNode;
      size++;
      return;
    }
  // traverse to current mid position
  while (--mid)
    {
      temp = temp->next;
    }

  newNode->next = temp->next;
  temp->next = newNode;
  size++;
}

int calcSize (struct Node *head)
{
  int size = 0;
  struct Node *temp = head;

  if (temp == NULL)
    return size;

  do
    {
      size++;
      temp = temp->next;

    }
  while (temp != head);

  return size;
}

void display (struct Node *head)
{
  // if there are no node in LL
  if (head == NULL)
    return;

  struct Node *temp = head;

  //need to take care of circular structure of LL
  do
    {
      printf ("%d ", temp->data);
      temp = temp->next;

    }
  while (temp != head);
  printf ("\n");
}

int main ()
{
  struct Node *head = NULL;

  insertStart (&head, 25);
  insertStart (&head, 5);

  display (head);

  insertMiddle (&head, 10);
  display (head);

  insertMiddle (&head, 20);
  display (head);

  insertMiddle (&head, 15);
  display (head);

  return 0;
}