Перемещение pop-up окна вместе с основным

#include <windows.h>

LONG APIENTRY   WndProc(HWND, UINT, WPARAM, LPARAM);
LONG APIENTRY WndProc2(HWND , UINT , WPARAM , LPARAM );

const char szWindowClass[] = "Windows";
const char szPopupWindowClass[] =  "Popup";
HWND hWndPopup;

int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)

{
    MSG msg;       
    HWND hWndMain;
    LPRECT rcParent;

WNDCLASS wc;

    wc.style        = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc  = (WNDPROC)WndProc;
    wc.cbClsExtra   = 0;
    wc.cbWndExtra   = 0;
    wc.hInstance    = hInstance;
    wc.hIcon        = LoadIcon(hInstance,IDI_APPLICATION);
    wc.hCursor      = LoadCursor(NULL,IDC_UPARROW);
    wc.hbrBackground    = (HBRUSH)(COLOR_WINDOW+10);
    wc.lpszMenuName = NULL;
    wc.lpszClassName    = szWindowClass;

WNDCLASS wpc;
   

    wpc.style       = CS_HREDRAW | CS_VREDRAW;
    wpc.lpfnWndProc = (WNDPROC)WndProc2;
    wpc.cbClsExtra  = 0;
    wpc.cbWndExtra  = 0;
    wpc.hInstance   = hInstance;
    wpc.hIcon       = LoadIcon(hInstance,IDI_APPLICATION);
    wpc.hCursor     = LoadCursor(NULL,IDC_UPARROW);
    wpc.hbrBackground   = (HBRUSH)(COLOR_WINDOW+10);
    wpc.lpszMenuName    = NULL;
    wpc.lpszClassName   = szPopupWindowClass;

//Step1. Registering Window Class
   
    if (!RegisterClass(&wc))
    {
MessageBox(NULL, "Window Registration Failed", "Error", MB_ICONEXCLAMATION | MB_OK);
        return 1;
    }

    if (!RegisterClass(&wpc))
    {
MessageBox(NULL, "Pop-up Window Registration Failed", "Error", MB_ICONEXCLAMATION | MB_OK);
        return 1;
    }
   
//Step 2:Finding the screen size

int a,a1;
a=   GetSystemMetrics(SM_CXSCREEN);
int b,b1;
b = GetSystemMetrics(SM_CYSCREEN);
a1 = a/3;
b1=b/3;

//Step 3: Creating the Window

    hWndMain = CreateWindow(szWindowClass,"Main window", WS_OVERLAPPEDWINDOW,0,b-b1,a1,b1,NULL, NULL, hInstance, NULL);

   if (!hWndMain)
   {
    MessageBox(NULL, "Window Creation Failed", "Error", MB_ICONEXCLAMATION | MB_OK);
        return 2;
   }

ShowWindow(hWndMain,nCmdShow);
UpdateWindow(hWndMain);


static  LPRECT rcMain;

//Step 4: Create the pop-up window


hWndPopup = CreateWindow(szPopupWindowClass,"POP-UP",WS_OVERLAPPEDWINDOW|WS_POPUP,(a1- (a1/4))-24,b-b1,a1/4,b1/4,NULL,NULL,hInstance,NULL);

if (!hWndPopup)
   {
    MessageBox(NULL, "Pop-up Window Creation Failed", "Error", MB_ICONEXCLAMATION | MB_OK);
        return 2;
   }
ShowWindow(hWndPopup,SW_HIDE);
UpdateWindow(hWndPopup);

//Step 5: The Message Loop
   
   while (GetMessage(&msg, NULL, 0, 0))
     DispatchMessage(&msg);
   
    return 0;

}

//The Window Procedure for popup-up window
   

LONG APIENTRY WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_RBUTTONDOWN:
        {
    ShowWindow(hWndPopup, SW_SHOW);
    UpdateWindow (hWndPopup);
    ShowWindow(hWnd,SW_SHOW);
    UpdateWindow(hWnd);
    break;
        }
    case WM_RBUTTONUP:
        {
    ShowWindow(hWndPopup, SW_HIDE);
    UpdateWindow (hWndPopup);
    ShowWindow(hWnd,SW_SHOW);
    UpdateWindow(hWnd);
    break;
        }  
????????????????????????????????????  
case WM_LBUTTONDOWN:
        {
    LPRECT rcMain;
    rcMain=(LPRECT)lParam;
    MoveWindow(hWnd,(rcMain->right/3),0,rcMain->right/3,rcMain->bottom,TRUE);
    ShowWindow(hWnd,SW_HIDE);
    return TRUE;
??????????????????????????????????????
        }
    case WM_CLOSE:
        DestroyWindow(hWnd);
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
   }
   return 0;

}

//Window Procedure for main window;
    HINSTANCE hInstance;
   
    LONG APIENTRY WndProc2(HWND hWndMain, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_CLOSE:
        DestroyWindow(hWndMain);
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWndMain, message, wParam, lParam);
   }
   return 0;

}