Implementing Circular Queue as Linked List ic C

#include <stdio.h>
#include <conio.h>
#include <malloc.h>
#include <windows.h>
/* structure containing a data part and link part */
struct node
{
 int data ;
 struct node * link ;
} ;
void addcirq ( struct node **, struct node **, int ) ;
int delcirq ( struct node **, struct node ** ) ;
void cirq_display ( struct node * ) ;
int main( )
{
 struct node *front, *rear ;
 front = rear = NULL ;
 addcirq ( &front, &rear, 10 ) ;
 addcirq ( &front, &rear, 17 ) ;
 addcirq ( &front, &rear, 18 ) ;
 addcirq ( &front, &rear, 5 ) ;
 addcirq ( &front, &rear, 30 ) ;
 addcirq ( &front, &rear, 15 ) ;
 system ( "cls" ) ;
 printf ( "Before deletion:\n" ) ;
 cirq_display ( front ) ;
 delcirq ( &front, &rear ) ;
 delcirq ( &front, &rear ) ;
 delcirq ( &front, &rear ) ;
 printf ( "After deletion:\n" ) ;
 cirq_display ( front ) ;
 return 0 ;
}
/* adds a new element at the end of queue */
void addcirq ( struct node **f, struct node **r, int item )
{
 struct node *q ;
 /* create new node */
 q = ( struct node * ) malloc ( sizeof ( struct node ) ) ;
 q -> data = item ;
 /* if the queue is empty */
 if ( *f == NULL )
  *f = q ;
 else
  ( *r ) -> link = q ;
 *r = q ;
 ( *r ) -> link = *f ;
}
/* removes an element from front of queue */
int delcirq ( struct node **f, struct node **r )
{
 struct node *q ;
 int item ;
 /* if queue is empty */
 if ( *f == NULL )
  printf ( "queue is empty\n" ) ;
 else
 {
  if ( *f == *r )
  {
   item = ( *f ) -> data ;
   free ( *f ) ;
   *f = NULL ;
   *r = NULL ;
  }
  else
  {
   /* delete the node */
   q = *f ;
   item = q -> data ;
   *f = ( *f ) -> link ;
   ( *r ) -> link = *f ;
   free ( q ) ;
  }
  return ( item ) ;
 }
 return NULL ;
}
/* displays whole of the queue */
void cirq_display ( struct node *f )
{
 struct node *q = f, *p = NULL ;
 /* traverse the entire linked list */
 while ( q != p )
 {
  printf ( "%d ", q -> data ) ;
  q = q -> link ;
  p = f ;
 }
 printf ( "\n" ) ;
}