c program for concatenation of two circularly linked lists

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

struct node
{
int info;
struct node *link;
};

struct node *create_list(struct node *last);
void display(struct node *last);
struct node *addtoempty(struct node *last,int data );
struct node *addatend(struct node *last,int data);
struct node *concat(struct node *last1,struct node *last2);

void main( )
{
struct node *last1=NULL,*last2=NULL;
last1=create_list(last1);
last2=create_list(last2);
printf("First list is :  ");
display(last1);
printf("Second list is :  ");
display(last2);
last1=concat(last1, last2);
printf("Concatenated list is  : ");
display(last1);
}

struct node *concat( struct node *last1,struct node *last2)
{
struct node *ptr;
if(last1==NULL)
{
 last1=last2;
 return last1;
}
if(last2==NULL )
 return last1;
ptr=last1->link;
last1->link=last2->link;
last2->link=ptr;
last1=last2;
return last1;
}
struct node *create_list(struct node *last)
{
int i,n;
int data;
printf("Enter the number of nodes : ");
scanf("%d",&n);
last=NULL;
if(n==0)
 return last;
printf("Enter the element to be inserted : ");
scanf("%d",&data);
last=addtoempty(last,data);

for(i=2;i<=n;i++)
{
 printf("Enter the element to be inserted : ");
 scanf("%d",&data);
 last=addatend(last,data);
}
return last;
}

void display(struct node *last)
{
struct node *p;
if(last==NULL)
{
 printf("List is empty\n");
 return;
}
p=last->link;  /*p points to first node*/
do
{
 printf("%d ", p->info);
 p=p->link;
}while(p!=last->link);
printf("\n");
}

struct node *addtoempty(struct node *last,int data)
{
struct node *tmp;
tmp = (struct node *)malloc(sizeof(struct node));
tmp->info = data;
last = tmp;
last->link = last;
return last;
}

struct node *addatend(struct node *last,int data)
{
struct node *tmp;
tmp = (struct node *)malloc(sizeof(struct node));
tmp->info = data;
tmp->link = last->link;
last->link = tmp;
last = tmp;
return last;
}