wn_select_screen(_c)

	status.i4.v = wn_select_screen(screen.i4.r)

	status.i4.v = wn_select_screen_c(screen.i4.v)

	This routine sets the output screen for graphic windows created by
	future calls to wn_view(_c).  This routine should only be called by
	Primary Application programs (PAs).  Actual screen I/O doesn't occur
	on the newly selected screen until the next call to wn_active(_c),
	wn_set_background_size_c, or wn_set_background_format_c.

	screen		output drawing screen
			(GXPA_1 -> number "1" graphics screen (default),
			 GXPA_2 -> number "2" graphics screen,
			 CLIB_DEFAULT_ARG -> simply return the current
					     screen value)

	This function returns ACNET status values as follows:

	CBS_INVARG		invalid screen value
	CBS_INVTYP		calling program is not a Primary Application
	GXPA_1			previous screen was graphics screen 1
	GXPA_2			precious screen was graphics screen 2

	This function requires the following include files:

	cnsparam_h, cbslib_h, acnet_errors_h

	Related functions:

	wn_screen_init(_c), wn_get_active_screen, wn_view(_c), wn_active(_c),
	intro_graphics_windows

	C/C++ usage:

	int	status;
	int	screen = GXPA_1;

	status = wn_select_screen_c(screen);