beginner DX question

#include <d3d9.h>LPDIRECT3D9 g_pD3D = NULL;LPDIRECT3DDEVICE9 g_pD3DDevice = NULL;HRESULT InitialiseD3D(HWND hWnd){    //First of all, create the main D3D object. If it is created successfully we     //should get a pointer to an IDirect3D8 interface.    g_pD3D = Direct3DCreate9(D3D_SDK_VERSION);    if(g_pD3D == NULL)    {        return E_FAIL;    }    //Get the current display mode    D3DDISPLAYMODE d3ddm;    if(FAILED(g_pD3D->GetAdapterDisplayMode(D3DADAPTER_DEFAULT, &d3ddm)))    {        return E_FAIL;    }    //Create a structure to hold the settings for our device    D3DPRESENT_PARAMETERS d3dpp;     ZeroMemory(&d3dpp, sizeof(d3dpp));    //Fill the structure.     //We want our program to be windowed, and set the back buffer to a format    //that matches our current display mode    d3dpp.Windowed = TRUE;    d3dpp.SwapEffect = D3DSWAPEFFECT_COPY_VSYNC;    d3dpp.BackBufferFormat = d3ddm.Format;    //Create a Direct3D device.    if(FAILED(g_pD3D->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hWnd,                                    D3DCREATE_SOFTWARE_VERTEXPROCESSING, &d3dpp, &g_pD3DDevice)))    {        return E_FAIL;    }        return S_OK;}void Render(){    if(g_pD3DDevice == NULL)    {        return;    }    //Clear the backbuffer to a green color    g_pD3DDevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0, 255, 0), 1.0f, 0);        //Begin the scene    g_pD3DDevice->BeginScene();        //Rendering of our game objects will go here        //End the scene    g_pD3DDevice->EndScene();        //Filp the back and front buffers so that whatever has been rendered on the back buffer    //will now be visible on screen (front buffer).    g_pD3DDevice->Present(NULL, NULL, NULL, NULL);}void CleanUp(){    if(g_pD3DDevice != NULL)    {        g_pD3DDevice->Release();        g_pD3DDevice = NULL;    }    if(g_pD3D != NULL)    {        g_pD3D->Release();        g_pD3D = NULL;    }}void GameLoop(){    //Enter the game loop    MSG msg;     BOOL fMessage;    PeekMessage(&msg, NULL, 0U, 0U, PM_NOREMOVE);        while(msg.message != WM_QUIT)    {        fMessage = PeekMessage(&msg, NULL, 0U, 0U, PM_REMOVE);        if(fMessage)        {            //Process message            TranslateMessage(&msg);            DispatchMessage(&msg);        }        else        {            //No message to process, so render the current scene            Render();        }    }}//The windows message handlerLRESULT WINAPI WinProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam){    switch(msg)    {        case WM_DESTROY:            PostQuitMessage(0);            return 0;        break;        case WM_KEYUP:             switch (wParam)            {                 case VK_ESCAPE:                    //User has pressed the escape key, so quit                    DestroyWindow(hWnd);                    return 0;                break;            }         break;    }    return DefWindowProc(hWnd, msg, wParam, lParam);}//Application entry pointINT WINAPI WinMain(HINSTANCE hInst, HINSTANCE, LPSTR, INT){    //Register the window class    WNDCLASSEX wc = {sizeof(WNDCLASSEX), CS_CLASSDC, WinProc, 0L, 0L,                      GetModuleHandle(NULL), NULL, NULL, NULL, NULL,                     "DX Project 1", NULL};    RegisterClassEx(&wc);    //Create the application's window    HWND hWnd = CreateWindow("DX Project 1", "www.andypike.com: Tutorial 1",                               WS_OVERLAPPEDWINDOW, 50, 50, 500, 500,                              GetDesktopWindow(), NULL, wc.hInstance, NULL);    //Initialize Direct3D    if(SUCCEEDED(InitialiseD3D(hWnd)))    {         //Show our window        ShowWindow(hWnd, SW_SHOWDEFAULT);        UpdateWindow(hWnd);        //Start game running: Enter the game loop        GameLoop();    }        CleanUp();    UnregisterClass("DX Project 1", wc.hInstance);        return 0;}