Nth last element in Linked List (C++)

The following code shows how to get nth last element in a linked list. It uses a queue to hold the temporary elements.

Algorithm:-
1>Make a queue of length N
2>Traverse the linked list from root
3>While traversing, en-queue first N elements
4>After this for en-queuing every element, de-queue another element.
5>When we reach the end of linked list, the last de-queued element will be the Nth last element.

/* 
 * File:   main.cpp
 * Author: Asit
 *
 * Created on 16 September, 2011, 12:25 AM
 */

#include <cstdlib>
#include <iostream>
#include <queue>

using namespace std;

struct node
{
    int data;
    node *next;
};

class LinkedList
{
    node *root;
public:
    LinkedList():root(NULL){}
    void add(int x)
    {
        node *temp = NULL;
                
        if(root==NULL)
        {
            root = new node;
            root->data = x;
            root->next = NULL;
        }
        else
        {
            temp = root;
            while(temp->next != NULL)
            {
                temp = temp->next;
            }
            
            temp->next = new node;
            temp = temp->next;
            temp->data = x;
            temp->next = NULL;
        }
    }
    
    void show()
    {
        node *temp = root;
        
        while(temp != NULL)
        {
            cout<<temp->data<<"  ";
            temp = temp->next;
        }
        cout<<endl;
    }
    
    int nthLast(int n)
    {
        queue<node*> t_queue;
        int i=1, t_data = -1;
        node *temp = root;
        
        while(temp != NULL)
        {
            t_queue.push(temp);
            if(i>=n)
            {
                t_data = (t_queue.front())->data; 
                t_queue.pop();
            }
            i++;
            temp = temp->next;
        }
        
        i--;
        if(i<n)
            cout<<"Linked list contains less than "<<n<<" elements"<<endl;
        
        return t_data;
    }
};

int main(int argc, char** argv) 
{
    LinkedList list;
    
    for(int i=0; i<20; i++)
        list.add(i*7+90);
    
    cout<<"Created linked list is .. "<<endl;
    list.show();
    
    cout<<"3rd last element : ";
    
    cout<<list.nthLast(3)<<endl;
    
    return 0;
}

Output:-

Created linked list is .. 
90  97  104  111  118  125  132  139  146  153  160  167  174  181  188  195  202  209  216  223  
3rd last element : 209