Write A Program For Merging Of Two Circular Lists

Program

   # 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)); /*
creates new node using
          data value passes as
            parameter and puts its
           address in the link field
           of last node of the
            existing list*/
           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");
    }
   struct node *merge(struct node *p, struct node *q)
        {
          struct node *temp=NULL;
          struct node *r=NULL;
          r = p;
          temp = p;
          while(temp->link != p)
               temp = temp->link;
          temp->link = q;
          temp = q;
          while( temp->link != q)
              temp = temp->link;
          temp->link = r;
         return(r);
   }

   void main()
   {
         int n;
         int x;
         struct node *start1=NULL ;
         struct node *start2=NULL;
         struct node *start3=NULL;

        /* this will create the first circular list nodes*/
         printf("Enter the number of nodes in the first list \n");
         scanf("%d",&n);
         while ( n-- > 0 )
         {
      printf( "Enter the data value to be placed in a node\n");
              scanf("%d",&x);
              start1 = insert ( start1, x );
         }
         printf("The first list is\n");
         printlist ( start1 );

         /* this will create the second circular list nodes*/
         printf("Enter the number of nodes in the second list \n");
         scanf("%d",&n);
         while ( n-- > 0 )
         {
      printf( "Enter the data value to be placed in a node\n");
             scanf("%d",&x);
             start2 = insert ( start2, x );
         }
         printf("The second list is:\n");
         printlist ( start2 );

         start3 = merge(start1,start2);
         printf("The resultant list is:\n");
         printlist(start3);
   }