Xcode C++, Cannot call pointer-returning method from main

Question

I'm trying to implement a LinkedList data structure. So I have main.cpp, LinkedListClass.cpp, and LinkedListClass.h

Here's my LinkedListClass.h

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

class LinkedListClass
{
public:
    Node* head;
    LinkedListClass();
    ~LinkedListClass();

    void insert(int value);
    void display();
    Node* ktoLast(Node* head, int k);//<-- this compile fine if I didn't call it from main

private:
    Node* tail;
};

I tried to call the ktoLast(Node* head, int k) method from main, here's how I did it:

int main(int argc, const char * argv[])
{
    LinkedListClass* myList = new LinkedListClass();

    myList->insert(3);
    myList->insert(4);
    myList->insert(2);
    myList->insert(7);
    myList->display();

    Node* head = myList->head;
    int k = 3;

    int val = myList->ktoLast(head, k)->data;
    cout << val << endl;


    return 0;
}

The error message:

===================UPDATE=========================

The method implementation

Node* ktoLast(Node* head, int k)
{
    Node* current = head;
    int length = 0;

    // find the length of the list
    while (current)
    {
        length++;
        current = current->next;
    }
    current = head; // reset back to head
    if (k > length || k < 1) return NULL;

    int count = 0;
    while (length - count != k)
    {
        count++;
        current = current->next;
    }

    return current;

}

Answer 1

The member function definition needs to be written as

Node* LinkedListClass::kToLast(Node* head, int k) { ...

What you have above is defining a free function with the same name. Also, if head is always the head of the current list (this)' it doesn't need to be passed as an argument.