' Leap year
FUNCTION leapyear(NUMBER y) TYPE NUMBER
   RETURN IIF(MOD(y, 4) = 0, IIF(MOD(y, 16) = 0, IIF(MOD(y, 100) != 0, TRUE, FALSE), TRUE), FALSE)
END FUNCTION

READ y
WHILE y != 0
    PRINT y, ": ", IIF$(leapyear(y), "", "not a "), "leapyear"
    READ y
WEND

DATA 1600, 1700, 1800, 1900, 1901, 1996, 2000, 2001, 2004, 0