Data Structures using C++

 #include< iostream.h > 
  #include< conio.h > 
  class cirdlink 
  { 
     struct node 
     { 
        int data; 
        node *rnext; 
        node *lnext; 
     }*new1,*head,*tail,*ptr,*temp; 
     public: 
     cirdlink() 
     { 
        head=tail=NULL; 
     } 
     void creation(); 
     void insertion(); 
     void deletion(); 
     void display(); 
   }; 
   void cirdlink :: creation() 
   { 
     if(head==NULL) 
     { 
        new1=new node[sizeof(node)]; 
        new1->rnext=NULL; 
        new1->lnext=NULL; 
        cout<<"enter student number :"; 
        cin>>new1->data; 
        head=new1; 
        tail=new1; 
        head->rnext=tail; 
        head->lnext=tail; 
        tail->rnext=head; 
        tail->lnext=head; 
      } 
      else 
        cout<<" creation done only once !"; 
   } 
   void cirdlink :: insertion() 
   { 
      int i,pos; 
      new1=new node[sizeof(node)]; 
      new1->rnext=NULL; 
      new1->lnext=NULL; 
      cout<<"enter student number :"; 
      cin>>new1->data; 
      cout<<"enter position you want to insert :"; 
      cin>>pos; 
      if(pos==1) 
      { 
        new1->rnext=head; 
        head=new1; 
        tail->lnext=head; 
        tail->rnext=head; 
        head->lnext=tail; 
      } 
      else 
      { 
        i=1; 
        temp=head; 
        while(i < pos-1 && temp->rnext!=tail) 
        { 
          i++; 
          temp=temp->rnext; 
        } 
        if(temp->rnext==tail) 
        { 
          new1->rnext=tail->rnext; 
          tail->rnext=new1; 
          new1->lnext=tail; 
          tail=new1; 
          head->lnext=tail; 
        } 
        else 
        { 
          new1->rnext=temp->rnext; 
          new1->lnext=temp; 
          temp->rnext=new1; 
          new1->rnext->lnext=new1; 
        } 
      } 
   } 
   void cirdlink :: deletion() 
   { 
      int pos,i; 
      cout<<"Enter Position you want to Delete ?"; 
      cin>>pos; 
      if(pos==1 && head!=tail) 
      { 
        ptr=head; 
        head=head->rnext; 
        head->lnext=tail; 
        tail->rnext=head; 
        delete ptr; 
      } 
      else 
      { 
        i=1; 
        temp=head; 
        while(i < pos-1 && temp->rnext!=tail) 
        { 
          i++; 
          temp=temp->rnext; 
        } 
        if(temp->rnext!=tail) 
        { 
          ptr=temp->rnext; 
          temp->rnext=ptr->rnext; 
          ptr->rnext->lnext=ptr->lnext; 
          delete ptr; 
        } 
        else 
        { 
          if(temp->rnext==tail && head!=tail) 
          { 
            ptr=tail; 
            tail=temp; 
            tail->rnext=head; 
            head->lnext=tail; 
            delete ptr; 
          } 
          else 
          { 
            head=NULL; 
            tail=NULL; 
            delete head; 
            delete tail; 
          } 
        } 
      } 
    } 
    void cirdlink::display() 
    { 
      int ch; 
      cout<<"1.forward 
      2.backward:"; 
      cout<<"Enter your choice<1/2>?"; 
      cin>>ch; 
      switch(ch) 
      { 
        case 1: if(head!=NULL) 
        { 
          temp=head; 
          while(temp!=tail) 
          { 
            cout<< temp->data<<" "; 
            temp=temp->rnext; 
          } 
          if(temp==tail) 
            cout<< temp->data; 
        } 
        break; 
        case 2 : if(tail!=NULL) 
        { 
          temp=tail; 
          while(temp!=head) 
          { 
            cout<< temp->data<<" "; 
            temp=temp->lnext; 
          } 
          if(temp==head) 
            cout<< temp->data; 
        } 
        break; 
      } 
    } 
    void main() 
    { 
      cirdlink c1; 
      int ch; 
      char op; 
      do 
      { 
        clrscr(); 
        cout<<"----------Menu------------"; 
        cout<<" 1.Creation 
        2.Insertion 
        3.Deletion 
        4.Display "; 
        cout<<"Enter Your choice <1..4> ?"; 
        cin>>ch; 
        switch(ch) 
        { 
          case 1 : c1.creation(); 
            break; 
          case 2 : c1.insertion(); 
            break; 
          case 3 : c1.deletion(); 
            break; 
          case 4 : c1.display(); 
            break; 
        } 
        cout<<"Do you want to continue < Y/N > ?"; 
        cin>>op; 
      }while(op=='y' || op=='Y'); 
      getch(); 
    }