linked list

I have the following code for a linked list. This code has one list and a user can enter values into the list then print it in order or reverse order. How would I change this code to create 5 link lists and the user can add values to the different linked lists?

#include <iostream.h>
#include <stdlib.h>
#include <string.h>

struct list_item
{
  char       string[50];
  list_item* next;
  list_item* previous;
};

class list
{
private:
  list_item* head;  // Ptr to head of list
  list_item* tail;  // Ptr to tail of list

public:
  list(); // Constructor - initialise empty list
  bool insert( char* );   // Add string to tail of list
  void display();         // Display list
  void display_reverse(); // Display list in reverse order
};

list::list()              // list constructor
{
  head = NULL;
  tail = NULL;
}

bool list::insert( char* data )
{
  list_item* new_item;
 
  new_item = new list_item;
  if ( new_item == NULL )
    return false;
  strcpy( new_item -> string, data );
 
  if ( head == NULL )
    {
      tail = new_item;
      head = new_item;
      new_item -> next = NULL;
      new_item -> previous = NULL;
    }
  else
    {
      tail -> next = new_item;
      new_item -> previous = tail;
      new_item -> next = NULL;
      tail = new_item;
    }
  return true;
}

void list::display()
{
  list_item* current;
  current = head;
  if ( current == NULL )
    cout << "\n\n Empty list!\n";
  else
    cout << "\n\n List:\n";

  while ( current != NULL )
    {
      cout << " " << current -> string << "\n";
      current = current -> next;
    }
}

void list::display_reverse()
{
  list_item* current;
  current = tail;
  if ( current == NULL )
    cout << "\n\n Empty list!\n";
  else
    cout << "\n\n List:\n";

  while ( current != NULL )
    {
      cout << " " << current -> string << "\n";
      current = current -> previous;
    }
}

void main( void )
{
  char string[50];
  char choice;
  list l;
  bool result;

  do {
    cout << "\n\n Menu:\n\n 1. Add to list\n 2. Print list\n";
    cout << " 3. Print list in reverse order\n 4. Quit\n\n Please enter your choice: ";
   
    cin >> choice;
   
    switch( choice )
      {
      case '1':
     cout << "\n Type string to add to list: ";
     cin >> string;
     result = l.insert( string );
     if ( !result )
       cout << "\n Insufficient memory!";
     break;
      case '2':
     l.display();
     break;
      case '3':
     l.display_reverse();
     break;
      }
  } while ( choice != '4' );
}