Days in the month

The Cal_days_in_month function is used to determine how many days are in a given calendar month for a specified year.  Although it may seem obvious that there are always 31 days in January, it's a good way to determine leap year.  You can also use this function when making a calendar so you don't need to save 11 different variables to sort through for the months that don't change their number of days.  Read more.