How to add new node once previous node has 3 values

So my title may be a little confusing, here is my question though. Say I have a number, 1083419 for arguments sake. I need to do two things with it, First - I would like to add these values into a linked list so that only three digits are in each node, so the number 1083419 would be:

Node = 001, Node = 083, Node = 419,

I am unsure how to make it so a new node is created when it reaches three digits, and I am also unsure how to pad the left node with 0's to make it three digits if it does not totally fill the node.

I have attached my code so far. In the long run, I eventually want to be able to add the two lists together into a third list, and print out the results of that.

Thanks in advance for anyones help.

Main.ccp file

#include <iostream>
#include "List.h"
using namespace std;


int main()
{

    List listA;           // Create object
    List listB;

    // New list to store the new total
    List listC;

    listA.addNode(90);
    listA.addNode(8);
    listA.addNode(100);

    listB.addNode(10);
    listB.addNode(8);

    int sum = listA.SumOfNodes (listA) + listB.SumOfNodes (listB);
    cout << sum << endl;

    listC.addNode(sum);
    cout << "The new list C is ";
    listC.printList();

    cout << endl;
    return 0;
}

List.h

#include <cstdlib>
#include <iostream>
using namespace std;


class List          // Create Linked List class
{
private:
    // List structure
    typedef struct node
    {
        int data;
        node* next;     // Create node pointer
    }*nodePtr;

    //typedef struct node* nodePtr;

    nodePtr head;
    nodePtr curr;
    nodePtr temp;

public:
    List();                             // Constructor
    void addNode(int addData);          // Adds node
    void deleteNode(int delData);       // Deletes Node
    int SumOfNodes(const List list1);   // Sum of Nodes
    void printList();                   // Prints list

}; // End class header

List.cpp

#include <iostream>
#include "List.h"
using namespace std;

List::List()                // Constructor
{
    head = NULL;            // Set all variables initially to NULL
    curr = NULL;
    temp = NULL;
}
//-----------------------------------------------------
//      ADD NODE FUNCTION
void List::addNode(int addData)
{
    nodePtr n = new node;
    n->next = NULL;         // Node n is pointing to, access its next element and make it point to NULL
    n->data = addData;

    if (head != NULL) {
        curr = head;
        while (curr->next != NULL) {
            curr = curr->next;
        }
        curr->next = n;
    }
    else {
        head = n;           // If list is not empty, n is the front
    }
}
//----------------------------------------------------
//      DELETE NODE FUNCTION
void List::deleteNode(int delData)       // Pass in data and traverse list 
{                                        // until delData matches the node value
    nodePtr delPtr = NULL;               // Then delete
    temp = head;
    curr = head;

    while (curr != NULL && curr->data != delData) {
        temp = curr;                    // Code to traverse the list
        curr = curr->next;
    }
    // If data is not in list, cout statement
    if (curr == NULL) {
        cout << delData << " was not in the list" << endl;
        delete delPtr;
    }
    else {
        delPtr = curr;
        curr = curr->next;
        temp->next = curr;      // Patches list after deletion

        if (delPtr == head) {
            head = head->next;
            temp = NULL;
        }

        delete delPtr;          // Deletes 
        cout << "The value " << delData << " has been deleted" << endl;
    }
}
//----------------------------------------------------
//      SUM OF NODES FUNCTION
// This function sums all the nodes together
int List::SumOfNodes(const List list1)
{
    //find the length of the list
    node *temp = head;
    int count = 0;

    while (temp != NULL)
    {
        count++;
        temp = temp->next;
    }

    //re-assign temp to head
    temp = head;

    //calculate the sum
    unsigned int sum = 0;

    for (unsigned int i = 1; i < pow(10, count); i = i * 10)
    {
        sum = sum + temp->data * i;
        temp = temp->next;
    }

    return sum;
}

//----------------------------------------------------
//      PRINT LIST FUNCTION
void List::printList()
{
    curr = head;
    while (curr != NULL) {
        cout << curr->data << endl;
        curr = curr->next;
    }
}