Returns the number of days in a month, based on the specified month and year
#include <Date.au3>
_DateDaysInMonth ( $iYear, $iMonthNum )
| $iYear | 4-digit year. |
| $iMonthNum | Month number (1 = January, 12 = December). |
| Success: | the number of days in the month. |
| Failure: | 0 and sets the @error flag to non-zero. |
| @error: | 1 - Invalid month number or year. |