Concatenating 2 Linked Lists end to end in C

#include <stdio.h>
#include <conio.h>
#include <malloc.h>
#include <windows.h>
struct node
{
 int data ;
 struct node *link ;
} ;
void append ( struct node **, int ) ;
void concat ( struct node **, struct node ** ) ;
void display ( struct node * ) ;
int count ( struct node * ) ;
struct node * erase ( struct node * ) ;
int main( )
{
 struct node *first, *second ;
 first = second = NULL ;  /* empty linked lists */
 append ( &first, 1 ) ;
 append ( &first, 2 ) ;
 append ( &first, 3 ) ;
 append ( &first, 4 ) ;
 system ( "cls" ) ;
 printf ( "First List:\n" ) ;
 display ( first ) ;
 printf ( "No. of elements in the first Linked List = %d\n", count ( first ) ) ;
 append ( &second, 5 ) ;
 append ( &second, 6 ) ;
 append ( &second, 7 ) ;
 append ( &second, 8 ) ;
 printf ( "Second List:\n" ) ;
 display ( second ) ;
 printf ( "No. of elements in the second Linked List = %d\n",
   count ( second ) ) ;
 /* the result obtained after concatenation is in the first list */
 concat ( &first, &second ) ;
 printf ( "Concatenated List:\n" ) ;
 display ( first ) ;
 printf ( "No. of elements in Linked List before erasing = %d\n",
   count ( first ) ) ;
 first = erase ( first ) ;
 printf ( "No. of elements in Linked List after erasing = %d\n",
   count ( first ) ) ;
 return 0 ;
}
/* adds a node at the end of a linked list */
void append ( struct node **q, int num )
{
 struct node *temp ;
 temp = *q ;
 if ( *q == NULL )  /* if the list is empty, create first node */
 {
  *q = ( struct node * ) malloc ( sizeof ( struct node ) ) ;
  temp = *q ;
 }
 else
 {
  /* go to last node */
  while ( temp -> link != NULL )
   temp = temp -> link ;
  /* add node at the end */
  temp -> link = ( struct node * ) malloc ( sizeof ( struct node ) ) ;
  temp = temp -> link ;
 }
 /* assign data to the last node */
 temp -> data = num ;
 temp -> link = NULL ;
}
/* concatenates two linked lists */
void concat ( struct node **p, struct node **q )
{
 struct node *temp ;
 /* if the first linked list is empty */
 if ( *p == NULL )
  *p = *q ;
 else
 {
  /* if both linked lists are non-empty */
  if ( *q != NULL )
  {
   temp = *p ;  /* points to the starting of the first list */
   /* traverse the entire first linked list */
   while ( temp -> link != NULL )
    temp = temp -> link ;
   temp -> link = *q ;  /* concatenate the second list after the
         first */
  }
 }
}
/* displays the contents of the linked list */
void display ( struct node *q )
{
 /* traverse the entire linked list */
 while ( q != NULL )
 {
  printf ( "%d ", q -> data ) ;
  q = q -> link ;
 }
 printf ( "\n\n" ) ;
}
/* counts the number of nodes present in the linked list */
int count ( struct node *q )
{
 int c = 0 ;
 /* traverse the entire linked list */
 while ( q != NULL )
 {
  q = q -> link ;
  c++ ;
 }
 return c ;
}
/* erases all the nodes from a linked list */
struct node * erase ( struct node *q )
{
 struct node *temp ;
 /* traverse till the end erasing each node */
 while ( q != NULL )
 {
  temp = q ;
  q = q -> link ;
  free ( temp ) ;  /* free the memory occupied by the node */
 }
 return NULL ;
}