C / C++ / MFC

The following steps describe a small sample code intended to demonstrate the behaviour previously described and nothing else.
A new empty win32 project was created.
A global variable was created to accommodate the bitmap handle:
HANDLE g_hBitmap;
The window style is registered in MyRegisterClass as
wcex.style = CS_DBLCLKS /*| CS_HREDRAW | CS_VREDRAW*/;
In InitInstance a bitmap is loaded after CreateWindow: 
g_hBitmap=LoadImage(0, // Load an OEM Image
TEXT("bitmap.bmp"),
IMAGE_BITMAP, // Type of image to be loadedd
0, // Uses the actual resource width
0, // Uses the actual resource height
LR_CREATEDIBSECTION|LR_LOADFROMFILE);
In the WndProc callback the following variables and references were defined to support the following code:
HDC hdcMem;
RECT rect;
LONG& width=rect.right; // rect.left=0 (see GetClientRect)
LONG& height=rect.bottom; // rect.top=0 (see GetClientRect)
In the WndProc callback the following code was inserted:
case WM_PAINT:
hdc = BeginPaint(hWnd, &ps);
GetClientRect(hWnd,&rect);
// Create a DC that matches the device
hdcMem=CreateCompatibleDC(hdc);
// Select the bitmap into the compatible DC
SelectObject(hdcMem, g_hBitmap);
BitBlt(hdc,0,0,width,height,hdcMem,0,0,SRCCOPY);
// Delete the Memory DC
DeleteDC(hdcMem);
EndPaint(hWnd, &ps);
break;
case WM_NCCALCSIZE:
if(wParam==TRUE) 
{
RECT r, ro;
NCCALCSIZE_PARAMS& s=*((NCCALCSIZE_PARAMS*)lParam);
// s.rgrc[0]: new window rect
// s.rgrc[1]: old window rect
// s.rgrc[2]: old client area
// new client area:
r.left=s.rgrc[2].left+(s.rgrc[0].left-s.rgrc[1].left);
r.right=s.rgrc[2].right+(s.rgrc[0].right-s.rgrc[1].right);
r.top=s.rgrc[2].top+(s.rgrc[0].top-s.rgrc[1].top);
r.bottom=s.rgrc[2].bottom+(s.rgrc[0].bottom-s.rgrc[1].bottom);
s.rgrc[0]=r; // return new client area
// check to see if something can be used from the old client area
if(IntersectRect(&ro,&r,&s.rgrc[2]))
{
// s.rgrc[1]: destination client rect
// s.rgrc[2]: source client rect
s.rgrc[1]=s.rgrc[2]=ro; // destination and source rectangles
return WVR_VALIDRECTS;
}
return 0;
}
else//wParam==FALSE
return DefWindowProc(hWnd,message,wParam,lParam); // wParam==FALSE
break;

int XLOW = 0;
int XHIGH = 10;
do 
	{
		n = rand()% (XHIGH - XLOW + 1) + XLOW;
                //for loop to check if value was 
                //previously used.
                //When I put the loop in it takes forever.
                //looking for an efficient way to check duplicates.
                //any suggetions?
		XHIGH--;
	} while (XHIGH != 0);