How to determine which day of a year belongs to what month? [closed]

问题

I'm a beginner and I gotta write a function in SML.

The assignment question is :

write a function named what_month that takes the number of a day (e.g., 257, assuming 365 days a year) as input, and returns the number of the month, that this day belongs to.

Example: what_month(40) should return 2 (February).

回答1:

for the simple case(that doesn't account for leap year), you can define a list of days in months months_days, and a recursive helper function aux, that takes an int called sum and an int list called numbers , and returns an int n such that the first n elements of the list add to less than sum, but the first n + 1 elements of the list add to sum or more.

val month_days= [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

fun what_month(day :int) =
 let  
   fun aux(sum :int,  numbers: int list) =
    let
      val numbers_tail = tl numbers
    in
      if sum <= (hd numbers)
      then 1
      else    
        1 + aux(sum, (hd numbers + hd numbers_tail)::(tl numbers_tail))
    end
 in
   aux(day, month_days)
 end

回答2:

One way of doing this could be to create a list of how many days there are in each month.

Such a list could look like this

days_in_month = [31, 28, 31, 30, ...]

Then you could easily count down your input number according to how many days each month has. When you reach a number which are smaller than the next months number of days, the input number must belong to the month you had reached.

Beware that this doesn't account for leap year. But that should not bee that difficult to work into it as well, if needed.

来源：https://stackoverflow.com/questions/15787541/how-to-determine-which-day-of-a-year-belongs-to-what-month

标签

functional-programming

sml