To do this using a function group:

REPORT demo_function_group_counter .

DATA number TYPE i VALUE 5.

CALL FUNCTION 'SET_COUNTER'
     EXPORTING
          set_value = number.

DO 3 TIMES.
  CALL FUNCTION 'INCREMENT_COUNTER'.
ENDDO.

CALL FUNCTION 'GET_COUNTER'
     IMPORTING
          get_value = number.

WRITE number.

Now to do it using a class....

Used objects and methods:
• cl_gui_splitter_container
• cl_gui_container
• cl_gui_toolbar
• cl_gui_column_tree
• handling application events (with triggering PAI)
• context menus

PROCESS BEFORE OUTPUT.
  MODULE PBO_100.
PROCESS AFTER INPUT.
  MODULE PAI_100.

Used objects and methods:
• cl_gui_splitter_container
• cl_gui_container
• cl_gui_toolbar
• cl_gui_list_tree
• handling application events (with triggering PAI)
• context menus

PROCESS BEFORE OUTPUT.
  MODULE PBO_100.
PROCESS AFTER INPUT.
  MODULE PAI_100.

This tiny program just displays the T001 table using grid control and all its default features.

Events:
• print events (see above)
• double_click
• toolbar
• user_command
• context_menu_request

Used object:
• cl_gui_alv_grid
• cl_gui_splitter_container
• cl_gui_container
• cl_gui_dialogbox_container
• cl_alv_event_toolbar_set (in event handler)
• cl_ctmenu (in event handler)

  GUI Status 'SCREEN_100' has 3 functions: BACK, EXIT and CANCEL of Type 'E' (Exit command), assigned to standard buttons: .
Screen 100 is empty:

PROCESS BEFORE OUTPUT.
  MODULE status_0100.
PROCESS AFTER INPUT.
  MODULE cancel AT EXIT-COMMAND.