Get screen resolution

You can call GetDeviceCaps(), but the figures are not always reliable on some systems. So, I prefer to use the two lines below, that give you the size of the screen in pixels.
RECT rc;
GetWindowRect(GetDesktopWindow(), &rc);

const long nScreenWidth = ::GetSystemMetrics(SM_CXSCREEN);
const long nScreenHeight = ::GetSystemMetrics(SM_CYSCREEN);