concatenate two circular linked lists

/* P3.9 Program to concatenate two circular 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);

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);
}/*End of main( )*/

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");
}/*End of display( )*/

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;
}/*End of addtoempty( )*/

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;
}/*End of addatend( )*/