C++ pagination example

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

/*
https://ideone.com/CHxrfS
You want to design the system so that sender tells what to do with action.
If you need some options that are not a part of the paginated menus then you
need to reserve senders for them. For example reserving from the beignning or end of the uint32 range a few values.

In this system sender is either a reserved ID or the page ID.
The action is either 0 or a valid item lowguid/ID.
*/

// This is a globally known value
// we want to substract the "next" and "previous" buttons from max items.
const int max_items = 32-2;

void ShowPage(int page, vector<int> const & items)
{
    // Clear menu()
    if (page < 0) // show main page if invalid page
        page = 0;
    int count = 0; // added items count
    for (int i = page*max_items; i < items.size(); ++i) // go through all items, we want to start from page beginning
    {
        // you want here that action is for example item lowguid.
        // you want to pass the page here so if something goes wrong you can show the same pageid on gossip select.
        printf("Some Item, sender: %i action: %i\n", page, items[i]);
        ++count; // added an item, increase count of items
        if (count >= max_items)
        {
            // we are at limit, add next button and stop adding items
            printf("Next page, sender: %i action: %i\n", page+1, 0);
            break;
        }
    }
    if (page > 0)
    {
        if (count == 0)
        {
            // player trying to view a page that doesnt contain any items and isnt main page.
            // We want to show the main menu here or show the previous page.
            ShowPage(page-1, items);
            return;
        }
        // we are at limit, add next button and stop adding items
        printf("Previous page, sender: %i action: %i\n", page-1, 0);
    }
    // Send menu()
}

int main() {
    /*
    Through for loops and such you have gathered all items the player has in a list called "items".
    These items can be for example pointers to the items you get from GetItemByPos or similar.
    These are all the valid items to be shown in the menu.
    */
    vector<int> items = {};
    int number_of_example_items = 32;
    for (int i = 1; i <= number_of_example_items; ++i)
        items.push_back(i);

    ShowPage(0, items);
    ShowPage(1, items);
    ShowPage(100, items);
}