Write program for Merging of two sorted lists

Program

# include <stdio.h>
# include <stdlib.h>
struct node
{
int data;
struct node *link;
};

struct node *merge (struct node *, struct node *);
struct node *insert(struct node *p, int n)
{
   struct node *temp;
   if(p==NULL)
   {
      p=(struct node *)malloc(sizeof(struct node));
      if(p==NULL)
      {
   printf("Error\n");
          exit(0);
      }
      p-> data = n;
      p-> link = NULL;
   }
   else
   {
      temp = p;
      while (temp-> link!= NULL)
      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 = NULL;
      }
      return (p);
   }

   void printlist ( struct node *p )
   {
      printf("The data values in the list are\n");
      while (p!= NULL)
         {
      printf("%d\t",p-> data);
           p = p-> link;
         }
   }
   /* a function to sort a list */
struct node *sortlist(struct node *p)
{
    struct node *temp1,*temp2,*min,*prev,*q;
   q = NULL;
   while(p != NULL)
   {
   prev = NULL;
      min = temp1 = p;
      temp2 = p -> link;
      while ( temp2 != NULL )
      {
   if(min -> data > temp2 -> data)
        {
   min = temp2;
           prev = temp1;
        }
        temp1 = temp2;
        temp2 = temp2-> link;
      }
   if(prev == NULL)
         p = min -> link;
         else
         prev -> link = min -> link;
         min -> link = NULL;
         if( q == NULL)
         q = min; /* moves the node with lowest data value in the list
pointed to by p to the list
   pointed to by q as a first node*/
         else
         {
            temp1 = q;
            /* traverses the list pointed to by q to get pointer to its
last node */
            while( temp1 -> link != NULL)
            temp1 = temp1 -> link;
            temp1 -> link = min; /* moves the node with lowest data value
in the list pointed to
   by p to the list pointed to by q at the end of list pointed by
   q*/
         }
      }
      return (q);
   }

   void main()
   {
      int n;
      int x;
      struct node *start1 = NULL ;
      struct node *start2 = NULL;
      struct node *start3 = NULL;
      /* The following code creates and sorts the first list */
      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);
      start1 = sortlist(start1);
      printf("The sorted list1 is\n");
      printlist ( start1 );
      /* the following creates and sorts the second list*/
      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);
      start2 = sortlist(start2);
      printf("The sorted list2 is\n");
      printlist ( start2 );
      start3 = merge(start1,start2);
      printf("The merged list is\n");
      printlist ( start3);
   }

   /* A function to merge two sorted lists */
   struct node *merge (struct node *p, struct node *q)
   {
      struct node *r=NULL,*temp;
      if (p == NULL)
           r = q;
      else
      if(q == NULL)
           r = p;
      else
         {
            if (p->data < q->data )
            {
   r = p;
   temp = p;
   p = p->link;
   temp->link = NULL;
              }
             else
              {
   r = q;
   temp =q;
   q =q->link;
   temp->link = NULL;
              }
              while((p!= NULL) && (q != NULL))
              {
                  if (p->data < q->data)
         {
         temp->link =p;
         p = p->link;
         temp =temp->link;
         temp->link =NULL;
         }
                     else
         {
            temp->link =q;
            q = q->link;
            temp =temp->link;
            temp->link =NULL;
            }
      }
         if (p!= NULL)
                 temp->link = p;
         if (q != NULL)
                 temp->link = q;
        }
   return( r) ;
   }