void print(struct student*head,int n)
 {struct student*p;
  printf("\n Now,These %d records are :\n",n);
  p=head;
  if(r->num!=NULL)
  do
    {printf("%ld,%s,%d,%c,%s,%s,%s\n\n",&p->num,p->name,&p->age,&p->sex,p->adr,p->tele,p->mail);
     p=p->next;
    } while(p->num!=NULL);
 }