i understanded this problem but i have one doubt that present below the actual program ,their is a temp pointer with allocating memory in while conditon they take that temp->link==null how it...

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

struct node
{
    int data;
    struct node *link;
};
 
struct node *insert(struct node *p, int n)
{
    struct node *temp;
    /* if the existing list is empty then insert a new node as the starting node */
    if(p==NULL)
    {
        p=(struct node *)malloc(sizeof(struct node)); /* creates new node data value passes as parameter */
        if(p==NULL)
        {
            printf("Error\n");
            exit(0);
        }
        p-> data = n;
        p-> link = p; /* makes the pointer pointing to itself because it is a circular list*/
    }
    else
    {
        temp = p;
        /* traverses the existing list to get the pointer to the last node of it */
        while (temp-> link != p)
            temp = temp-> link;
        temp-> link = (struct node *)malloc(sizeof(struct node)); 
        if(temp -> link == NULL)
        {
            printf("Error\n");
            exit(0);
        }
        temp = temp-> link;
        temp-> data = n;
        temp-> link = p;
    }
    return (p);
}
 
   void printlist ( struct node *p )
   {
   struct node *temp;
    temp = p;
   printf("The data values in the list are\n");
      if(p!= NULL)
      {
      do
            {
            printf("%d\t",temp->data);
            temp=temp->link;
            } while (temp!= p);
      }
      else
         printf("The list is empty\n");
   }
 
   void main()
   {
      int n;
      int x;
      struct node *start = NULL ;
 
      printf("Enter the nodes to be created \n");
      scanf("%d",&n);
      while ( n -- > 0 )
      {
   printf( "Enter the data values to be placed in a node\n");
         scanf("%d",&x);
         start = insert ( start, x );
      }
      printf("The created list is\n");
      printlist ( start );
 
   }

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 else
      {
      temp = p;
   /* traverses the existing list to get the pointer to the last node of it */
      while (temp-> link != p)
         temp = temp-> link;
            temp-> link = (struct node *)malloc(sizeof(struct node)); 
           if(temp -> link == NULL)
           {
         printf("Error\n");
              exit(0);
           }
           temp = temp-> link;
           temp-> data = n;
           temp-> link = p;
          }
          return (p);
   }