API Windows problème (C + +, VS08)

//Windows Example Code
//Matthew Bett 2005
 
#include <windows.h>
#include <stdio.h>
#include <mmsystem.h>
#include <math.h>
 
#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480
 
/* not using any mouse input
typedef struct Mouse{
  int x,y;
} Mouse;
*/
 
typedef struct Sprite{
  int x, y, width, height;
  HBITMAP bitmap;
} Sprite;
 
int xpos, ypos;
int ticker = 0;
 
HBITMAP theOldFrontBitMap, theOldBackBitMap;
HWND ghwnd;
RECT screenRect;
HDC backHDC, frontHDC, bitmapHDC;   //Hardware device contexts for the Buffers
 
bool keys[256];
 
Sprite TestSprite;
 
BOOL waitFor(unsigned long delay);
 
 
LRESULT CALLBACK WndProc(HWND,UINT,WPARAM,LPARAM);
 
void RegisterMyWindow(HINSTANCE hInstance){
  WNDCLASSEX  wcex;                          
 
  wcex.cbSize = sizeof(wcex);
  wcex.style = CS_HREDRAW | CS_VREDRAW;
  wcex.lpfnWndProc = WndProc;
  wcex.cbClsExtra = 0;
  wcex.cbWndExtra = 0;
  wcex.hInstance = hInstance;
  wcex.hIcon = 0;
  wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
               
  wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
  wcex.lpszMenuName = NULL;
  wcex.lpszClassName = L" FirstWindowClass";
  wcex.hIconSm = 0;
 
  RegisterClassEx(&wcex);
}
 
 
BOOL InitialiseMyWindow(HINSTANCE hInstance, int nCmdShow){
  HWND hwnd;
  hwnd = CreateWindow(L" FirstWindowClass", L" Double Buffering", WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU,
  CW_USEDEFAULT, CW_USEDEFAULT, SCREEN_WIDTH, SCREEN_HEIGHT, NULL,   NULL, hInstance,
  NULL);                     
  if(!hwnd) return FALSE;
 
  ShowWindow(hwnd, nCmdShow);                
  UpdateWindow(hwnd);  
  ghwnd = hwnd;
  return TRUE;
}
 
 
 
BOOL WaitFor(unsigned long delay){
  static unsigned long clockStart = 0;
  unsigned long timePassed;
  unsigned long now = timeGetTime();
 
  timePassed = now - clockStart;
  if(timePassed > delay){
    clockStart = now;
    return TRUE;
  } //why was there an else here? <!-- s;) --><img src=\"{SMILIES_PATH}/icon_wink.gif\" alt=\";)\" title=\"Wink\"><!-- s;) -->
  return FALSE;
}
 
LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam){
  switch(message){                                         
    case WM_CREATE:  
    break;
 
    case WM_SIZE:
    break;
 
    case WM_KEYDOWN:
    keys[wParam]=true;
    break;
 
    case WM_KEYUP:
    keys[wParam]=false;
    break;
 
    /*
    case WM_MOUSEMOVE:
    MousePos.x = LOWORD (lParam);
    MousePos.y = HIWORD (lParam);
    break;
    */
 
    case WM_PAINT:
    break;
 
    case WM_DESTROY:
    PostQuitMessage(0);
    break;
  }
 
  return DefWindowProc(hwnd, message, wParam, lParam);
}
 
HBITMAP LoadABitmap(LPCWSTR szFileName){
  return (HBITMAP)LoadImage(NULL, szFileName, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
}
 
void drawSprite(Sprite theSprite){
  HBITMAP originalBitMap;
  originalBitMap = (HBITMAP)SelectObject(bitmapHDC,theSprite.bitmap);
  BitBlt(backHDC,theSprite.x,theSprite.y,theSprite.x+theSprite.width,theSprite.y+theSprite.height,bitmapHDC,0,0,SRCCOPY);
  SelectObject(bitmapHDC,originalBitMap);
}
 
void setBuffers(){
  GetClientRect(ghwnd, &screenRect); //creates rect based on window client area
  frontHDC = GetDC(ghwnd); // Initialises front buffer device context (window)
  backHDC = CreateCompatibleDC(frontHDC); // sets up Back DC to be compatible with the front
  bitmapHDC=CreateCompatibleDC(backHDC);
  theOldFrontBitMap = CreateCompatibleBitmap(frontHDC, screenRect.right,
  screenRect.bottom); //creates bitmap compatible with the front buffer
  theOldBackBitMap = (HBITMAP)SelectObject(backHDC, theOldFrontBitMap);
  //creates bitmap compatible with the back buffer
  FillRect(backHDC, &screenRect, (HBRUSH)GetStockObject(0));   
}
 
void displayFrame(){
  BitBlt(frontHDC, screenRect.left,screenRect.top, screenRect.right,
  screenRect.bottom, backHDC, 0, 0, SRCCOPY);
  FillRect(backHDC, &screenRect, (HBRUSH)GetStockObject(0));   
}
 
void releaseResources(){
  SelectObject(backHDC,theOldBackBitMap);
  DeleteDC(backHDC);
  DeleteDC(bitmapHDC);
  ReleaseDC(ghwnd,frontHDC);
}
 
/*
  classes
*/
 
//player ship
class Player{
  public:
  int x,y,height,width;
  float vSpeed,maxVSpeed,acceleration,friction;
  bool visible;
  Sprite sprite;
 
  //constructor
  Player(int setX, int setY, LPCWSTR bmp, int w, int h){
    sprite.bitmap = LoadABitmap(bmp);
    sprite.x = setX;
    sprite.y = setY;
    sprite.width = w;
    sprite.height = h;
    x = setX;
    y = setY;
    visible = true;
    vSpeed = 0;
    maxVSpeed = 14;
    acceleration = 1.3;
    friction = 0.7;
  }
 
  //every frame
  void step(){
    /*
      basic movement physics
    */
 
    //up
    if(keys[87]){
      //if not moving too fast upwards
      if(vSpeed > -maxVSpeed){
        //accelerate up
        vSpeed -= acceleration;
        //cap speed
        if(vSpeed < -maxVSpeed) vSpeed = -maxVSpeed;
      }
    }
    //down
    if(keys[83]){
      //if not moving too fast downwards
      if(vSpeed < maxVSpeed){
        //accelerate down
        vSpeed += acceleration;
        //cap speed
        if(vSpeed > maxVSpeed) vSpeed = maxVSpeed;
      }
    }
 
    //friction
    if(vSpeed > 0){
      vSpeed -= friction;
      if(vSpeed < 0) vSpeed = 0;
    } else if(vSpeed < 0){
      vSpeed += friction;
      if(vSpeed > 0) vSpeed = 0;
    }
 
 
    //apply motion
    y += vSpeed;
 
    //don't go out of the screen
    if(y < 0){
      vSpeed = 0;
      y = 0;
    } else if(y > 428){
      vSpeed = 0;
      y = 428;
    }
  }
 
  void draw(){
    if(!visible)
      return;
    sprite.x = x;
    sprite.y = y;
    drawSprite(sprite);
  }
};
 
 
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
  PSTR szCmdLine, int nCmdShow){                         
  MSG msg;
  HDC hdcWindow;
 
  //create the player
  Player player(50,SCREEN_HEIGHT/2,L" icon.bmp",32,32);
 
  RegisterMyWindow(hInstance);
 
  if(!InitialiseMyWindow(hInstance, nCmdShow))
    return FALSE;
 
  setBuffers();
  while(TRUE){                   
    if (PeekMessage(&msg,NULL,0,0,PM_REMOVE)){
      if(msg.message==WM_QUIT)
        break;
 
      TranslateMessage(&msg);                  
      DispatchMessage(&msg);
    } else if(WaitFor(10)){  
      //step the player
      player.step();
      //draw the player
      player.draw();
         
      displayFrame();  
    }
  }
 
  releaseResources();
  return msg.wParam;                           
}