kolibrios/programs/develop/oberon07/Samples/Windows/Console/Doors.ob07

(*
   adapted to Oberon-07 by 0CodErr, KolibriOS team
                                                   *)
(*
   There are 100 doors in a row that are all initially closed.
   You make 100 passes by the doors.
   The first time through, visit every door and toggle the door (if the door is closed, open it; if it is open, close it).
   The second time, only visit every 2nd door (door #2, #4, #6, ...), and toggle it.
   The third time, visit every 3rd door (door #3, #6, #9, ...), etc, until you only visit the 100th door.
   What state are the doors in after the last pass? Which are open, which are closed?
*)
MODULE Doors;

IMPORT In, Out, Console;


CONST
    CLOSED = FALSE;
    OPEN   = TRUE;


TYPE
    List = ARRAY 101 OF BOOLEAN;


VAR
    Doors: List;
    I, J:  INTEGER;


BEGIN
    Console.open;

    FOR I := 1 TO 100 DO
        FOR J := 1 TO 100 DO
            IF J MOD I = 0 THEN
                IF Doors[J] = CLOSED THEN
                    Doors[J] := OPEN
                ELSE
                    Doors[J] := CLOSED
                END
            END
        END
    END;
    FOR I := 1 TO 100 DO
        Out.Int(I, 3);
        Out.String(" is ");
        IF Doors[I] = CLOSED THEN
            Out.String("Closed.")
        ELSE
            Out.String("Open.")
        END;
        Out.Ln
    END;
    In.Ln;

    Console.exit(TRUE)
END Doors.