C Program for Insertion at the nth node of Singly Linked List

//Linked list insertion at specific position in C
#include<stdio.h>
#include<stdlib.h>

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

// required for insertAfter
int getCurrSize (struct Node *node)
{
  int size = 0;

  while (node != NULL)
    {
      node = node->next;
      size++;
    }
  return size;
}

//function to insert after nth node
void insertPosition (int pos, int data, struct Node **head)
{
  int size = getCurrSize (*head);

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

  // Can't insert if position to insert is greater than size of Linked List
  // can insert after negative pos
  if (pos < 0 || pos > size)
    printf ("Invalid position to insert\n");

  // inserting first node
  else if (pos == 0)
    {
      newNode->next = *head;
      *head = newNode;
    }

  else
    {
      // temp used to traverse the Linked List
      struct Node *temp = *head;

      // traverse till the nth node
      while (--pos)
	temp = temp->next;

      // assign newNode's next to nth node's next
      newNode->next = temp->next;
      // assign nth node's next to this new node
      temp->next = newNode;
      // newNode inserted b/w 3rd and 4th node
    }
}

void display (struct Node *node)
{

  printf ("Linked List : ");

  // as linked list will end when Node is Null
  while (node != NULL)
    {
      printf ("%d ", node->data);
      node = node->next;
    }
  printf ("\n");
}

int main ()
{

  //creating 4 pointers of type struct Node
  //So these can point to address of struct type variable
  struct Node *head = NULL;
  struct Node *node2 = NULL;
  struct Node *node3 = NULL;
  struct Node *node4 = NULL;

  // allocate 3 nodes in the heap 
  head = (struct Node *) malloc (sizeof (struct Node));
  node2 = (struct Node *) malloc (sizeof (struct Node));
  node3 = (struct Node *) malloc (sizeof (struct Node));
  node4 = (struct Node *) malloc (sizeof (struct Node));


  head->data = 10;		// data set for head node 
  head->next = node2;		// next pointer assigned to address of node2 

  node2->data = 20;
  node2->next = node3;

  node3->data = 30;
  node3->next = node4;

  node4->data = 40;
  node4->next = NULL;


  display (head);

  //Inserts data: 15 after the 1st node
  insertPosition (1, 15, &head);

  //Inserts data: 25 after the 3rd node
  insertPosition (3, 25, &head);

  //Inserts data: 35 after the 5th node
  insertPosition (5, 35, &head);

  //Inserts data: 25 after the 7th node
  insertPosition (7, 45, &head);

  display (head);

  // Invalid: can't insert after -2 pos
  insertPosition (-2, 100, &head);

  // Invalid: Current size 8, trying to enter after 10th pos
  insertPosition (10, 200, &head);

  return 0;
}