>There is a way to know how many days I have in specific month(29/30/31)?
(for example I call the fanction ?func?({09/09/2006})

Here's my two-cents worth:

FUNCTION DayInMonth
LPARAMETERS pnMonth
RETURN DAY(GOMONTH(DTOC(TRANSFORM(pnMonth)+"/01/"+TRANSFORM(YEAR())),1)-1)

Above code takes a month number as input and does the following:

1. Convert pnMonth to a date value for first of month
2. Goes to first day of next month
3. Subtracts one day for the last day of month input
4. Uses DAY() function to get the number of the days and returns value