Days between dates

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Revision as of 04:56, 28 July 2021 by Laurence (talk | contribs) (Added Fōrmulæ solution)
Days between dates is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.
Task

Calculate the number of days between two dates.

Date input should be of the form   YYYY-MM-DD.


Motivation

To demonstrate one of the numerous ways this can be done.

Ada

<lang Ada>with Ada.Calendar; with Ada.Text_IO; with Ada.Integer_Text_IO;

with GNAT.Calendar.Time_IO;

procedure Days_Between_Dates is 

  function Days_Between (Lower_Date  : in Ada.Calendar.Time;
                         Higher_Date : in Ada.Calendar.Time) return Integer
  is
     use Ada.Calendar;
     Diff : constant Duration := Higher_Date - Lower_Date;
  begin
     return Integer (Diff / Day_Duration'Last);
  end Days_Between;

  procedure Put_Days_Between (Lower_Date  : in String;
                              Higher_Date : in String;
                              Comment     : in String)
  is
     use Ada.Text_IO;
     use Ada.Integer_Text_IO;
     use GNAT.Calendar.Time_IO;

     Diff : constant Integer := Days_Between (Lower_Date  => Value (Lower_Date),
                                              Higher_Date => Value (Higher_Date));
  begin
     Put ("Days between " & Lower_Date & " and " & Higher_Date & " is ");
     Put (Diff, Width => 5);
     Put (" days  --  ");
     Put (Comment);
     New_Line;
  end Put_Days_Between;

begin 

  Put_Days_Between ("1995-11-21", "1995-11-21", "Identical dates");
  Put_Days_Between ("2019-01-01", "2019-01-02", "Positive span");
  Put_Days_Between ("2019-01-02", "2019-01-01", "Negative span");
  Put_Days_Between ("2019-01-01", "2019-03-01", "Non-leap year");
  Put_Days_Between ("2020-01-01", "2020-03-01", "Leap year");
  Put_Days_Between ("1902-01-01", "1968-12-25", "Past");
  Put_Days_Between ("2090-01-01", "2098-12-25", "Future");
  Put_Days_Between ("1902-01-01", "2098-12-25", "Long span");

end Days_Between_Dates;</lang>

Output:
Days between 1995-11-21 and 1995-11-21 is     0 days  --  Identical dates
Days between 2019-01-01 and 2019-01-02 is     1 days  --  Positive span
Days between 2019-01-02 and 2019-01-01 is    -1 days  --  Negative span
Days between 2019-01-01 and 2019-03-01 is    59 days  --  Non-leap year
Days between 2020-01-01 and 2020-03-01 is    60 days  --  Leap year
Days between 1902-01-01 and 1968-12-25 is 24465 days  --  Past
Days between 2090-01-01 and 2098-12-25 is  3280 days  --  Future
Days between 1902-01-01 and 2098-12-25 is 71947 days  --  Long span

AppleScript

<lang applescript>on daysBetweenDates(date1, date2) 

   considering numeric strings -- Allows for leading zeros having been omitted.
       if (date1 = date2) then return date1 & " and " & date2 & " are the same date"
   end considering
   
   -- Get the components of each date.
   set astid to AppleScript's text item delimiters
   set AppleScript's text item delimiters to "-"
   set {y1, m1, d1} to date1's text items
   set {y2, m2, d2} to date2's text items
   set AppleScript's text item delimiters to astid
   
   -- Derive AppleScript date objects.
   -- The best way to do this generally is to use the 'current date' function to obtain a date object
   -- and then to set the properties of the result (or of a copy) to the required values.
   -- The initial setting of the day values to 1 is to prevent overflow due to possibly
   -- incompatible day and month values during the sequential setting of the properties.
   -- The integer values set here are automatically coerced from the text values obtained above.
   tell (current date) to set {its day, its year, its month, its day, its time, firstDate} to {1, y1, m1, d1, 0, it}
   copy firstDate to secondDate
   tell secondDate to set {its day, its year, its month, its day} to {1, y2, m2, d2}
   
   -- Do the math.
   set daysDifference to (firstDate - secondDate) div days
   
   -- Format some output.
   if (daysDifference > 0) then
       return date1 & " comes " & daysDifference & " day" & item (((daysDifference is 1) as integer) + 1) of {"s", ""} & ¬
           " after " & date2
   else
       return date1 & " comes " & -daysDifference & " day" & item (((daysDifference is -1) as integer) + 1) of {"s", ""} & ¬
           " before " & date2
   end if

end daysBetweenDates

return daysBetweenDates("2020-04-11", "2001-01-01") & linefeed & ¬ 

   daysBetweenDates("2020-04-11", "2020-04-12") & linefeed & ¬
   daysBetweenDates("2020-04-11", "2020-04-11")</lang>
Output:
"2020-04-11 comes 7040 days after 2001-01-01
2020-04-11 comes 1 day before 2020-04-12
2020-04-11 and 2020-04-11 are the same date"


Or, composing a function from reusable generics, and drawing on NSISO8601DateFormatter:

<lang applescript>use AppleScript version "2.4" use framework "Foundation" use scripting additions


-- daysBetween :: String -> String -> Int on daysBetween(iso8601From, iso8601To) 

   set midnight to "T00:00:00+00:00"
   ((dateFromISO8601(iso8601To & midnight) - ¬
       dateFromISO8601(iso8601From & midnight)) / 86400) as integer

end daysBetween


-- dateFromISO8601 :: String -> Date on dateFromISO8601(isoDateString) 

   set ca to current application
   tell ca's NSISO8601DateFormatter's alloc's init()
       set its formatOptions to ¬
           (ca's NSISO8601DateFormatWithInternetDateTime as integer)
       (its dateFromString:(isoDateString)) as date
   end tell

end dateFromISO8601


TEST----------------------------

on run 

   script test
       on |λ|(ab)
           set {a, b} to ab
           set delta to daysBetween(a, b)
           (a & " -> " & b & " -> " & ¬
               justifyRight(5, space, delta as string)) & ¬
               pluralize(delta, " day")
       end |λ|
   end script
   
   unlines(map(test, {¬
       {"2020-04-11", "2001-01-01"}, ¬
       {"2020-04-11", "2020-04-12"}, ¬
       {"2020-04-11", "2020-04-11"}, ¬
       {"2019-01-01", "2019-09-30"}}))

end run


GENERIC FUNCTIONS ---------------------

-- Absolute value. -- abs :: Num -> Num on abs(x) 

   if 0 > x then
       -x
   else
       x
   end if

end abs


-- justifyRight :: Int -> Char -> String -> String on justifyRight(n, cFiller, strText) 

   if n > length of strText then
       text -n thru -1 of ((replicate(n, cFiller) as text) & strText)
   else
       strText
   end if

end justifyRight


-- map :: (a -> b) -> [a] -> [b] on map(f, xs) 

   -- The list obtained by applying f
   -- to each element of xs.
   tell mReturn(f)
       set lng to length of xs
       set lst to {}
       repeat with i from 1 to lng
           set end of lst to |λ|(item i of xs, i, xs)
       end repeat
       return lst
   end tell

end map


-- mReturn :: First-class m => (a -> b) -> m (a -> b) on mReturn(f) 

   -- 2nd class handler function lifted into 1st class script wrapper. 
   if script is class of f then
       f
   else
       script
           property |λ| : f
       end script
   end if

end mReturn


-- pluralize :: Int -> String -> String on pluralize(n, s) 

   set m to abs(n)
   if 0 = m or 2 ≤ m then
       s & "s"
   else
       s
   end if

end pluralize


-- replicate :: Int -> String -> String on replicate(n, s) 

   set out to ""
   if n < 1 then return out
   set dbl to s
   
   repeat while (n > 1)
       if (n mod 2) > 0 then set out to out & dbl
       set n to (n div 2)
       set dbl to (dbl & dbl)
   end repeat
   return out & dbl

end replicate


-- unlines :: [String] -> String on unlines(xs) 

   -- A single string formed by the intercalation
   -- of a list of strings with the newline character.
   set {dlm, my text item delimiters} to ¬
       {my text item delimiters, linefeed}
   set str to xs as text
   set my text item delimiters to dlm
   str

end unlines</lang>

Output:
2020-04-11 -> 2001-01-01 -> -7040 days
2020-04-11 -> 2020-04-12 ->     1 day
2020-04-11 -> 2020-04-11 ->     0 days
2019-01-01 -> 2019-09-30 ->   272 days

Arturo

Translation of: Ruby

<lang rebol>daysBetweenDates: function [startDate, endDate][ 

   a: to :date.format: "dd/MM/yyyy" startDate
   b: to :date.format: "dd/MM/yyyy" endDate

   return abs b\days - a\days

]

print [ 

   "days between the two dates:" 
   daysBetweenDates "01/01/2019" "19/10/2019"

]</lang>

Output:
days between the two dates: 291

AWK

<lang AWK>

  1. syntax: GAWK -f DAYS_BETWEEN_DATES.AWK

BEGIN { 

   regexp = "^....-..-..$" # YYYY-MM-DD
   main("1969-12-31","1970-01-01","builtin has bad POSIX start date")
   main("1970-01-01","2038-01-19","builtin has bad POSIX stop date")
   main("1970-01-01","2019-10-02","format OK")
   main("1970-01-01","2019/10/02","format NG")
   main("1995-11-21","1995-11-21","identical dates")
   main("2019-01-01","2019-01-02","positive date")
   main("2019-01-02","2019-01-01","negative date")
   main("2019-01-01","2019-03-01","non-leap year")
   main("2020-01-01","2020-03-01","leap year")
   exit(0)

} function main(date1,date2,comment, d1,d2,diff) { 

   printf("\t%s\n",comment)
   d1 = days_builtin(date1)
   d2 = days_builtin(date2)
   diff = (d1 == "" || d2 == "") ? "error" : d2-d1
   printf("builtin %10s to %10s = %s\n",date1,date2,diff)
   d1 = days_generic(date1)
   d2 = days_generic(date2)
   diff = (d1 == "" || d2 == "") ? "error" : d2-d1
   printf("generic %10s to %10s = %s\n",date1,date2,diff)

} function days_builtin(ymd) { # use gawk builtin 

   if (ymd !~ regexp) { return("") }
   if (ymd < "1970-01-01" || ymd > "2038-01-18") { return("") } # outside POSIX range
   gsub(/-/," ",ymd)
   return(int(mktime(sprintf("%s 0 0 0",ymd)) / (60*60*24)))

} function days_generic(ymd, d,m,y,result) { # use Python formula 

   if (ymd !~ regexp) { return("") }
   y = substr(ymd,1,4)
   m = substr(ymd,6,2)
   d = substr(ymd,9,2)
   m = (m + 9) % 12
   y = int(y - int(m/10))
   result = 365*y + int(y/4) - int(y/100) + int(y/400) + int((m*306+5)/10) + (d-1)
   return(result)

} </lang>

Output:
    builtin has bad POSIX start date
builtin 1969-12-31 to 1970-01-01 = error
generic 1969-12-31 to 1970-01-01 = 1
    builtin has bad POSIX stop date
builtin 1970-01-01 to 2038-01-19 = error
generic 1970-01-01 to 2038-01-19 = 24855
    format OK
builtin 1970-01-01 to 2019-10-02 = 18171
generic 1970-01-01 to 2019-10-02 = 18171
    format NG
builtin 1970-01-01 to 2019/10/02 = error
generic 1970-01-01 to 2019/10/02 = error
    identical dates
builtin 1995-11-21 to 1995-11-21 = 0
generic 1995-11-21 to 1995-11-21 = 0
    positive date
builtin 2019-01-01 to 2019-01-02 = 1
generic 2019-01-01 to 2019-01-02 = 1
    negative date
builtin 2019-01-02 to 2019-01-01 = -1
generic 2019-01-02 to 2019-01-01 = -1
    non-leap year
builtin 2019-01-01 to 2019-03-01 = 59
generic 2019-01-01 to 2019-03-01 = 59
    leap year
builtin 2020-01-01 to 2020-03-01 = 60
generic 2020-01-01 to 2020-03-01 = 60

C

<lang C>

  1. include<stdbool.h>
  2. include<string.h>
  3. include<stdio.h>

typedef struct{ 

   int year, month, day;

}date;

date extractDate(char* str){ 

   return (date){.year = 1000 * (str[0]-'0') + 100 * (str[1]-'0') + 10 * (str[2]-'0') + (str[3]-'0'), .month = 10*(str[5]-'0') + (str[6]-'0'), .day = 10*(str[8]-'0') + (str[9]-'0')};

}

bool isValidDate(char* str){ 

   date newDate;
   
   if(strlen(str)!=10 && str[4]!='-' && str[7]!='-'){
       return false;
   }

   newDate = extractDate(str);

   if(newDate.year<=0 || newDate.month<=0 || newDate.day<=0 || newDate.month>12 || (newDate.month==2 && newDate.day>29) || 
     ((newDate.month==1 || newDate.month==3 || newDate.month==5 || newDate.month==7 || newDate.month==8 || newDate.month==10 || newDate.month==12) && newDate.day>31) || 
     newDate.day>30 || (newDate.year%4==0 && newDate.month==2 && newDate.month>28)){
         return false;
     }

   return true;

}

int diffDays(date date1,date date2){ 

   int days1, days2;
   
   date1.month = (date1.month + 9)%12;
   date1.year = date1.year - date1.month/10;

   date2.month = (date2.month + 9)%12;
   date2.year = date2.year - date2.month/10;

   days1 = 365*date1.year + date1.year/4 - date1.year/100 + date1.year/400 + (date1.month*306 + 5)/10 + ( date1.day - 1 );
   days2 = 365*date2.year + date2.year/4 - date2.year/100 + date2.year/400 + (date2.month*306 + 5)/10 + ( date2.day - 1 );

   return days2 - days1;

}

int main(int argc,char** argv) { 

   if(argc!=3){
       return printf("Usage : %s <yyyy-mm-dd> <yyyy-mm-dd>",argv[0]);
   }

   if(isValidDate(argv[1])&&isValidDate(argv[2]) == false){
       return printf("Dates are invalid.\n");
   }

   printf("Days Difference : %d\n", diffDays(extractDate(argv[1]),extractDate(argv[2])));

   return 0;

} </lang> Output : 

abhishek_ghosh@Azure:~/doodles$ ./a.out 2019-01-01 2019-12-02
Days Difference : 335

C++

Translation of: c

<lang cpp>#include <iomanip>

  1. include <iostream>

class Date { private: 

   int year, month, day;

public: 

   Date(std::string str) {
       if (isValidDate(str)) {
           year = atoi(&str[0]);
           month = atoi(&str[5]);
           day = atoi(&str[8]);
       } else {
           throw std::exception("Invalid date");
       }
   }

   int getYear() {
       return year;
   }

   int getMonth() {
       return month;
   }

   int getDay() {
       return day;
   }

   // YYYY-MM-DD
   static bool isValidDate(std::string str) {
       if (str.length() != 10 || str[4] != '-' || str[7] != '-') {
           return false;
       }

       if (!isdigit(str[0]) || !isdigit(str[1]) || !isdigit(str[2]) || !isdigit(str[3])) {
           return false; // the year is not valid
       }
       if (!isdigit(str[5]) || !isdigit(str[6])) {
           return false; // the month is not valid
       }
       if (!isdigit(str[8]) || !isdigit(str[9])) {
           return false; // the day is not valid
       }

       int year = atoi(&str[0]);
       int month = atoi(&str[5]);
       int day = atoi(&str[8]);

       // quick checks
       if (year <= 0 || month <= 0 || day <= 0) {
           return false;
       }
       if (month > 12) {
           return false;
       }

       switch (month) {
       case 2:
           if (day > 29) {
               return false;
           }
           if (!isLeapYear(year) && day == 29) {
               return false;
           }
           break;
       case 1:
       case 3:
       case 5:
       case 7:
       case 8:
       case 10:
       case 12:
           if (day > 31) {
               return false;
           }
           break;
       default:
           if (day > 30) {
               return false;
           }
           break;
       }

       return true;
   }

   static bool isLeapYear(int year) {
       if (year > 1582) {
           return ((year % 4 == 0) && (year % 100 > 0))
               || (year % 400 == 0);
       }
       if (year > 10) {
           return year % 4 == 0;
       }
       // not bothering with earlier leap years
       return false;
   }

   friend std::ostream &operator<<(std::ostream &, Date &);

};

std::ostream &operator<<(std::ostream &os, Date &d) { 

   os << std::setfill('0') << std::setw(4) << d.year << '-';
   os << std::setfill('0') << std::setw(2) << d.month << '-';
   os << std::setfill('0') << std::setw(2) << d.day;
   return os;

}

int diffDays(Date date1, Date date2) { 

   int d1m = (date1.getMonth() + 9) % 12;
   int d1y = date1.getYear() - d1m / 10;

   int d2m = (date2.getMonth() + 9) % 12;
   int d2y = date2.getYear() - d2m / 10;

   int days1 = 365 * d1y + d1y / 4 - d1y / 100 + d1y / 400 + (d1m * 306 + 5) / 10 + (date1.getDay() - 1);
   int days2 = 365 * d2y + d2y / 4 - d2y / 100 + d2y / 400 + (d2m * 306 + 5) / 10 + (date2.getDay() - 1);

   return days2 - days1;

}

int main() { 

   std::string ds1 = "2019-01-01";
   std::string ds2 = "2019-12-02";

   if (Date::isValidDate(ds1) && Date::isValidDate(ds2)) {
       Date d1(ds1);
       Date d2(ds2);
       std::cout << "Days difference : " << diffDays(d1, d2);
   } else {
       std::cout << "Dates are invalid.\n";
   }

   return 0;

}</lang>

Output:
Days difference : 335

Alternative using Boost

Library: Boost

<lang cpp>#include <cstdlib>

  1. include <iostream>
  2. include <boost/date_time/gregorian/gregorian.hpp>

int main(int argc, char** argv) { 

   using namespace boost::gregorian;
   if (argc != 3) {
       std::cerr << "usage: " << argv[0] << " start-date end-date\n";
       return EXIT_FAILURE;
   }
   try {
       date start_date(from_simple_string(argv[1]));
       date end_date(from_simple_string(argv[2]));
       std::cout << end_date - start_date << '\n';
   } catch (const std::exception& ex) {
       std::cerr << ex.what() << '\n';
       return EXIT_FAILURE;
   }
   return EXIT_SUCCESS;

}</lang>

Output:
./days_between_dates 2020-01-01 2020-09-06
249

C#

<lang csharp>using System; using System.Globalization;

public class Program { 

   public static void Main() => WriteLine(DateDiff("1970-01-01", "2019-10-18"));

   public static int DateDiff(string d1, string d2) {
       var a = DateTime.ParseExact(d1, "yyyy-MM-dd", CultureInfo.InvariantCulture);
       var b = DateTime.ParseExact(d2, "yyyy-MM-dd", CultureInfo.InvariantCulture);
       return (int)(b - a).TotalDays;
   }

}</lang>

Output:
18187

COBOL

Works with: GnuCOBOL

<lang COBOL>COBOL *> days-between 

     *> Tectonics: cobc -xj days-between.cob

      identification division.
      program-id. days-between.

      procedure division.
      compute tally = 
        function integer-of-formatted-date('YYYY-MM-DD', '2019-11-24')
        -
        function integer-of-formatted-date('YYYY-MM-DD', '2000-01-01')
      display tally

      compute tally = 
        function integer-of-formatted-date('YYYYMMDD', '20191124')
        -
        function integer-of-formatted-date('YYYYMMDD', '20000101')
      display tally

      goback.
      end program days-between.</lang>
Output:
prompt$ cobc -xj days-between-dates.cob
07267
07267

D

<lang d>import std.datetime.date; import std.stdio;

void main() { 

   auto fromDate = Date.fromISOExtString("2019-01-01");
   auto toDate = Date.fromISOExtString("2019-10-07");
   auto diff = toDate - fromDate;
   writeln("Number of days between ", fromDate, " and ", toDate, ": ", diff.total!"days");

}</lang>

Output:
Number of days between 2019-Jan-01 and 2019-Oct-07: 279

Delphi

Library: System.SysUtils
Translation of: C#

<lang Delphi> program Days_between_dates;

{$APPTYPE CONSOLE}

uses 

 System.SysUtils;

function CreateFormat(fmt: string; Delimiter: Char): TFormatSettings; begin 

 Result := TFormatSettings.Create();
 with Result do
 begin
   DateSeparator := Delimiter;
   ShortDateFormat := fmt;
 end;

end;

function DaysBetween(Date1, Date2: string): Integer; var 

 dt1, dt2: TDateTime;
 fmt: TFormatSettings;

begin 

 fmt := CreateFormat('yyyy-mm-dd', '-');
 dt1 := StrToDate(Date1, fmt);
 dt2 := StrToDate(Date2, fmt);
 Result := Trunc(dt2 - dt1);

end;

begin 

 Writeln(DaysBetween('1970-01-01', '2019-10-18'));
 readln;

end.</lang>

Output:
18187

Erlang

<lang erlang>

-module(daysbetween). -export([between/2,dateToInts/2]).

% Return Year or Month or Date from datestring dateToInts(String, POS) -> 

 list_to_integer( lists:nth( POS, string:tokens(String, "-") ) ).

% Alternative form of above % dateToInts(String,POS) -> % list_to_integer( lists:nth( POS, re:split(String ,"-", [{return,list},trim]) ) ).

% Return the number of days between dates formatted "2019-09-30" between(DateOne,DateTwo) -> 

 L = [1,2,3],
 [Y1,M1,D1] =  [ dateToInts(DateOne,X) || X <- L],
 [Y2,M2,D2] =  [ dateToInts(DateTwo,X) || X <- L],
 GregOne = calendar:date_to_gregorian_days(Y1,M1,D1),
 GregTwo = calendar:date_to_gregorian_days(Y2,M2,D2),
 GregTwo - GregOne.

</lang>

Output:

erlang shell: 

30> c(daysbetween).
c(daysbetween).
{ok,daysbetween}
31> daysbetween:between("2019-01-01", "2019-09-30").
daysbetween:between("2019-01-01", "2019-09-30").
272

Excel

LAMBDA

Excel dates are numbers counting days since the start of January 1900, and arithmetic operations can be applied to them directly.

(Unless entered as strings, they differ from other numbers only in the display format applied to the containing cell).

The lambda expression below maps over an array of date strings, defining a new array of the differences, in units of one day, between today's date and those earlier dates.

(See LAMBDA: The ultimate Excel worksheet function)

Works with: Office 365 betas 2021
Output:

The formula in cell B2 defines the array of day counts which populate the range B2:B5

fx =LAMBDA(dateString, TODAY() - DATEVALUE(dateString) )(C2#)
A B C D
1 Difference in days Earlier date Today
2 39020 1914-07-28 2021-05-27
3 37088 1919-11-11
4 29916 1939-07-01
5 27661 1945-09-02

Alternatively, we can express the same mapping over the whole C2# array by directly writing:

fx = TODAY() - DATEVALUE(C2#)
A B C D
1 Difference in days Earlier date Today
2 39020 1914-07-28 2021-05-27
3 37088 1919-11-11
4 29916 1939-07-01
5 27661 1945-09-02

F#

<lang fsharp> // Days between dates: Nigel Galloway. June 3rd., 2021 let n,g=System.DateTime.Parse("1792-9-22"),System.DateTime.Parse("1805-12-31") printfn "There are %d days between %d-%d-%d and %d-%d-%d" (g-n).Days n.Year n.Month n.Day g.Year g.Month g.Day </lang>

Output:
There are 4847 days between 1792-9-22 and 1805-12-31

Factor

Factor supports the addition and subtraction of timestamps and durations with the time+ and time- words. <lang factor>USING: calendar calendar.parser kernel math prettyprint ;

days-between ( ymd-str ymd-str -- n )
   [ ymd>timestamp ] bi@ time- duration>days abs ;

"2019-01-01" "2019-09-30" days-between . "2016-01-01" "2016-09-30" days-between .  ! leap year</lang>

Output:
272
273

Frink

Frink handles dates and intervals between dates robustly, including time zones. The sample below could use minutes or seconds instead of days.

Frink can even track leap seconds as they are added to the calendar if desired. The code d1-d2 in the sample below could be replaced by subtractLeap[d1,d2] to obtain exact counts of seconds between dates.

See Frink's Date/Time Handling documentation to see how easy it is to work with dates, times, timezones, calendrical systems, and even leap seconds correctly and easily.

<lang frink>d1 = # 2020-12-25 # d2 = # 2020-12-06 # println[d1-d2 -> days]</lang>

Output:
19

Fōrmulæ

Fōrmulæ programs are not textual, visualization/edition of programs is done showing/manipulating structures but not text. Moreover, there can be multiple visual representations of the same program. Even though it is possible to have textual representation —i.e. XML, JSON— they are intended for storage and transfer purposes more than visualization and edition.

Programs in Fōrmulæ are created/edited online in its website, However they run on execution servers. By default remote servers are used, but they are limited in memory and processing power, since they are intended for demonstration and casual use. A local server can be downloaded and installed, it has no limitations (it runs in your own computer). Because of that, example programs can be fully visualized and edited, but some of them will not run if they require a moderate or heavy computation/memory resources, and no local server is being used.

In this page you can see the program(s) related to this task and their results.

Go

<lang go>package main

import ( 

   "fmt"
   "log"
   "time"

)

const layout = "2006-01-02" // template for time.Parse

// Parameters assumed to be in YYYY-MM-DD format. func daysBetween(date1, date2 string) int { 

   t1, err := time.Parse(layout, date1)
   check(err)
   t2, err := time.Parse(layout, date2)
   check(err)
   days := int(t1.Sub(t2).Hours() / 24)
   if days < 0 {
       days = -days
   }
   return days

}

func check(err error) { 

   if err != nil {
       log.Fatal(err)
   }

}

func main() { 

   date1, date2 := "2019-01-01", "2019-09-30"
   days := daysBetween(date1, date2)
   fmt.Printf("There are %d days between %s and %s\n", days, date1, date2)

   date1, date2 = "2015-12-31", "2016-09-30"
   days = daysBetween(date1, date2)
   fmt.Printf("There are %d days between %s and %s\n", days, date1, date2)

}</lang>

Output:
There are 272 days between 2019-01-01 and 2019-09-30
There are 274 days between 2015-12-31 and 2016-09-30

Groovy

Translation of: Kotlin
Translation of: Java

<lang groovy>import java.time.LocalDate

def fromDate = LocalDate.parse("2019-01-01") def toDate = LocalDate.parse("2019-10-19") def diff = fromDate - toDate println "Number of days between ${fromDate} and ${toDate}: ${diff}"</lang>

Output:
Number of days between 2019-01-01 and 2019-10-19: 291

Haskell

<lang Haskell>import Data.Time (Day) import Data.Time.Calendar (diffDays) import Data.Time.Format (parseTimeM,defaultTimeLocale)

main = do 

   putStrLn $ task "2019-01-01" "2019-09-30"
   putStrLn $ task "2015-12-31" "2016-09-30"

task :: String -> String -> String task xs ys = "There are " ++ (show $ betweenDays xs ys) ++ " days between " ++ xs ++ " and " ++ ys ++ "."

betweenDays :: String -> String -> Integer betweenDays date1 date2 = go (stringToDay date1) (stringToDay date2) 

   where
   go (Just x) (Just y) = diffDays y x
   go Nothing _ = error "Exception: Bad format first date"
   go _ Nothing = error "Exception: Bad format second date"

stringToDay :: String -> Maybe Day stringToDay date = parseTimeM True defaultTimeLocale "%Y-%-m-%-d" date</lang>

Output:
There are 272 days between 2019-01-01 and 2019-09-30.
There are 274 days between 2015-12-31 and 2016-09-30.

J

   require'~addons/types/datetime/datetime.ijs'
   2021 03 16 daysDiff 1960 05 04
22231

   vectorize=: [: evaluate hyphen_to_space
   hyphen_to_space=: (=&'-')`(,:&' ')}
   evaluate=: ".
   but_first=: &


   '2021-03-16' daysDiff but_first vectorize  '1960-05-04'
22231

Java

Translation of: Kotlin

<lang java>import java.time.LocalDate; import java.time.temporal.ChronoUnit;

public class DaysBetweenDates { 

   public static void main(String[] args) {
       LocalDate fromDate = LocalDate.parse("2019-01-01");
       LocalDate toDate = LocalDate.parse("2019-10-19");
       long diff = ChronoUnit.DAYS.between(fromDate, toDate);
       System.out.printf("Number of days between %s and %s: %d\n", fromDate, toDate, diff);
   }

}</lang>

Output:
Number of days between 2019-01-01 and 2019-10-19: 291

Julia

<lang julia>using Dates

@show Day(DateTime("2019-09-30") - DateTime("2019-01-01"))

@show Day(DateTime("2019-03-01") - DateTime("2019-02-01"))

@show Day(DateTime("2020-03-01") - DateTime("2020-02-01"))

@show Day(DateTime("2029-03-29") - DateTime("2019-03-29"))

</lang>

Output:
Day(DateTime("2019-09-30") - DateTime("2019-01-01")) = 272 days
Day(DateTime("2019-03-01") - DateTime("2019-02-01")) = 28 days
Day(DateTime("2020-03-01") - DateTime("2020-02-01")) = 29 days
Day(DateTime("2029-03-29") - DateTime("2019-03-29")) = 3653 days

Kotlin

<lang scala>import java.time.LocalDate import java.time.temporal.ChronoUnit

fun main() { 

   val fromDate = LocalDate.parse("2019-01-01")
   val toDate = LocalDate.parse("2019-10-19")
   val diff = ChronoUnit.DAYS.between(fromDate, toDate)
   println("Number of days between $fromDate and $toDate: $diff")

}</lang>

Output:
Number of days between 2019-01-01 and 2019-10-19: 291

Lua

This uses os.difftime to compare two Epoch times. Not to be used with dates before 1970. <lang lua>SECONDS_IN_A_DAY = 60 * 60 * 24

-- Convert date string as YYYY-MM-DD to Epoch time. function parseDate (str) 

 local y, m, d = string.match(str, "(%d+)-(%d+)-(%d+)")
 return os.time({year = y, month = m, day = d})

end

-- Main procedure io.write("Enter date 1: ") local d1 = parseDate(io.read()) io.write("Enter date 2: ") local d2 = parseDate(io.read()) local diff = math.ceil(os.difftime(d2, d1) / SECONDS_IN_A_DAY) print("There are " .. diff .. " days between these dates.")</lang>

Output:
Enter date 1: 1970-01-01
Enter date 2: 2019-10-02
There are 18171 days between these dates.

Mathematica / Wolfram Language

<lang Mathematica>DateDifference["2020-01-01", "2020-03-01"] DateDifference["2021-01-01", "2021-03-01"]</lang>

Output:
Quantity[60, "Days"]
Quantity[59, "Days"]

Nim

<lang Nim>import times

proc daysBetween(date1, date2: string): int64 = 

 const Fmt = initTimeFormat("yyyy-MM-dd")
 (date2.parse(Fmt, utc()) - date1.parse(Fmt, utc())).inDays

const Dates = [("1995-11-21","1995-11-21"), 

              ("2019-01-01","2019-01-02"),
              ("2019-01-02","2019-01-01"),
              ("2019-01-01","2019-03-01"),
              ("2020-01-01","2020-03-01"),
              ("1902-01-01","1968-12-25"),
              ("2090-01-01","2098-12-25")]

for (date1, date2) in Dates: 

 echo "Days between ", date1, " and ", date2, ": ", daysBetween(date1, date2)</lang>
Output:
Days between 1995-11-21 and 1995-11-21: 0
Days between 2019-01-01 and 2019-01-02: 1
Days between 2019-01-02 and 2019-01-01: -1
Days between 2019-01-01 and 2019-03-01: 59
Days between 2020-01-01 and 2020-03-01: 60
Days between 1902-01-01 and 1968-12-25: 24465
Days between 2090-01-01 and 2098-12-25: 3280

Perl

Would not reinvent this wheel. <lang perl>use feature 'say'; use Date::Calc qw(Delta_Days);

say Delta_Days(2018,7,13, 2019,9,13); # triskaidekaphobia say Delta_Days(1900,1,1, 2000,1,1); # a century say Delta_Days(2000,1,1, 2100,1,1); # another, with one extra leap day say Delta_Days(2020,1,1, 2019,10,1); # backwards in time say Delta_Days(2019,2,29, 2019,3,1); # croaks</lang>

Output:
427
36524
36525
-92
Date::Calc::PP::Delta_Days(): Date::Calc::Delta_Days(): not a valid date at Days_between_dates line 10

Phix

Library: Phix/basics
include builtins\timedate.e 
-- specify as many or as few permitted formats as you like:
set_timedate_formats({"YYYY-MM-DD","DD/MM/YYYY","YYYY/MM/DD"})
 
constant SECONDS_TO_DAYS = 60*60*24
 
procedure test(string d1, d2, desc="")
    timedate td1 = parse_date_string(d1),
             td2 = parse_date_string(d2)
    atom s = timedate_diff(td1,td2,DT_DAY),
         d = s/SECONDS_TO_DAYS
    string e = elapsed(s)&desc
    printf(1,"Days between %s and %s: %d [%s]\n",{d1,d2,d,e})
end procedure
test("1969-12-31","1970-01-01")
test("1995-11-21","1995-11-21",", same date")
test("2019-01-02","2019-01-01",", negative date")
test("2019-01-01","2019-03-01",", non-leap year")
test("2020-01-01","2020-03-01",", leap year")
test("1970-01-01", "2019/10/18")
test("1970-01-01", "18/10/2019")

As shown, timedate_diff() can optionally round to the nearest whole number of days [else omit DT_DAY].
Note that elapsed() assumes all years are exactly 365 days, and in no way takes leap years into consideration (as opposed, of course, to timedate_diff() which handles them flawlessly), not that you sh/c/would ever use the string output of elapsed() in any further calculations anyway.

Output:
Days between 1969-12-31 and 1970-01-01: 1 [1 day]
Days between 1995-11-21 and 1995-11-21: 0 [0s, same date]
Days between 2019-01-02 and 2019-01-01: -1 [minus 1 day, negative date]
Days between 2019-01-01 and 2019-03-01: 59 [59 days, non-leap year]
Days between 2020-01-01 and 2020-03-01: 60 [60 days, leap year]
Days between 1970-01-01 and 2019/10/18: 18187 [49 years, 302 days]
Days between 1970-01-01 and 18/10/2019: 18187 [49 years, 302 days]

PicoLisp

<lang PicoLisp>(de diffDates (A B) 

  (abs (- ($dat A "-") ($dat B "-"))) )

(println (diffDates "2019-1-1" "2019-9-30")) (println (diffDates "2015-12-31" "2016-09-30"))</lang>

Output:
272
274


Python

<lang python>

  1. !/usr/bin/python

import sys

Difference between two dates = g(y2,m2,d2) - g(y1,m1,d1) 

   Where g() gives us the Gregorian Calendar Day
   Inspired  by discussion at:
   https://stackoverflow.com/questions/12862226/the-implementation-of-calculating-the-number-of-days-between-2-dates

def days( y,m,d ): 

  input year and month are shifted to begin the year in march
 m = (m + 9) % 12 
 y = y - m/10

  with (m*306 + 5)/10 the number of days from march 1 to the current 'm' month 
 result = 365*y + y/4 - y/100 + y/400 + (m*306 + 5)/10 + ( d - 1 )
 return result

def diff(one,two): 

 [y1,m1,d1] = one.split('-')
 [y2,m2,d2] = two.split('-')
 # strings to integers
 year2 = days( int(y2),int(m2),int(d2))
 year1 = days( int(y1), int(m1), int(d1) )
 return year2 - year1

if __name__ == "__main__": 

 one = sys.argv[1]
 two = sys.argv[2]
 print diff(one,two)

</lang>

Output:
python days-between.py 2019-01-01 2019-09-30
272

Raku

(formerly Perl 6) Dates are first class objects in Raku and may have arithmetic in days done directly on them. <lang perl6>say Date.new('2019-09-30') - Date.new('2019-01-01');

say Date.new('2019-03-01') - Date.new('2019-02-01');

say Date.new('2020-03-01') - Date.new('2020-02-01');

say Date.new('2029-03-29') - Date.new('2019-03-29');

say Date.new('2019-01-01') + 90;

say Date.new('2020-01-01') + 90;

say Date.new('2019-02-29') + 30;

CATCH { default { .message.say; exit; } };</lang> 

272
28
29
3653
2019-04-01
2020-03-31
Day out of range. Is: 29, should be in 1..28

REBOL

REBOL accepts a multitude of lexically recognized date! formats. date! is a builtin datatype. Slashes or dashes, year-month-day, day/month/year, or dd/monthname/year, etc. Math on dates defaults to days. 

prompt$ rebol -q
>> 2019-11-24 - 2000-01-01
== 7267
>> 2019-nov-24 - 01-jan-2000
== 7267

REXX

Works with: Regina REXX

bare bones version

Programming note:   the   B   (Base)   an option for the   date   BIF which indicates to compute the number of
days since the beginning of the Gregorian calendar,   and   I   which is the option that indicates the date is in
the   ISO   (International Standards Organization standard 8601:2004)   format. <lang rexx>/*REXX program computes the number of days between two dates in the form of YYYY-MM-DD */ parse arg $1 $2 . /*get 2 arguments (dates) from the C.L.*/ say abs( date('B',$1,"I") - date('B',$2,"I") ) ' days between ' $1 " and " $2 

                                                /*stick a fork in it,  we're all done. */</lang>
output   when using the inputs of:     2019-10-02   2000-01-01 
7214  days between  2019-10-02  and  2000-01-01

supports more variations

This REXX version supports more variations in the date format   (allows a single digit month and/or day), as well as
allowing a single asterisk   (*)   to be used for a date   (which signifies that the current date is to be used).

The dates may be specified in the following formats: 

       ,            (a comma)        indicates today's date
       *            (an asterisk)    indicates today's date 
       yyyy-mm-dd   where yyyy may be a 2- or 4-digit year, mm may be a 1- or 2-digit month, dd may be a 1- or 2-digit day of month
       mm/dd/yyyy   (as above)
       mm/dd        (as above),  but the current year is assumed
       dd\mm\yyyy   (as above)
       dd\mm        (as above),  but the current year is assumed



Commas   (,)   are inserted into numbers where appropriate.

Also, more informative error messages are generated. <lang rexx>/*REXX program computes the number of days between two dates in the form of YYYY-MM-DD */ parse arg $.1 $.2 _ . 1 . . xtra /*obtain two arguments from the C.L. */ seps= '/-\'; yr.= .; mon.= .; dd.= . /*define the defaults for both dates. */ 

           do a=1  for 2                        /*process both of the specified dates. */
           if $.a== | $.a=="*" | $.a==','  then $.a= date("I")
              do s=1  for length(seps)          /*process a specified date by separator*/
              sep= substr(seps, s, 1)           /*obtain one of the supported sep char.*/
              if pos(sep, $.a)\==0  then call conv $.a         /*parse the date string.*/
              end   /*s*/
           end      /*a*/

?.1= '1st' ?.2= '2nd' if _ \== then call err "too many arguments specified: " xtra dy.= 31 /*default number of days for all months*/ parse value 30 with dy.4 1 dy.6 1 dy.9 1 dy.11 /*define 30─day months, Feb. is special*/ @notCorr= "isn't in a support date format: " /*used for a literal for an error msg. */ 

 do j=1  for 2                                  /*examine both dates for correct format*/
 if $.j           ==  then call err ?.j "date was not specified."
 if length(yr.j)==0     then call err ?.j "year"  @notCorr '(missing)'
 if isDec(yr.j)         then call err ?.j "year"  @notCorr '(has a non─decimal digit)'
 if yr.j<1 | yr.j>9999  then call err ?.j "year"  @notCorr '(not in the range 1──►9999)'
 if length(mon.j)==0    then call err ?.j "month" @notCorr '(missing)'
 if isDec(mon.j)        then call err ?.j "month" @notCorr '(has a non─decimal digit)'
 if mon.j<1 | mon.j>12  then call err ?.j "month" @notCorr '(not in the range 1──►12)'
 if length(dd.j)==0     then call err ?.j "day"   @notCorr '(missing)'
 if isDec(dd.j)         then call err ?.j "day"   @notCorr '(has a non─decimal digit)'
 mo= mon.j
 if leapYr(yr.j)  then dy.2= 29                 /*Is it a leapyear? Use 29 days for Feb*/
                  else dy.2= 28                 /*Isn't "     "      "  28   "   "   " */
 if dd.j<1 | dd.j>dy.mo then call err ?.j "day"   @notCorr '(day in month is invalid)'

   yr.j= right( yr.j  +0, 4, 0)                 /*force YYYY to be four decimal digits.*/
  mon.j= right(mon.j  +0, 2, 0)                 /*  "    MON  "  "  two    "       "   */
   dd.j= right( dd.j  +0, 2, 0)                 /*  "     DD  "  "   "     "       "   */
    $.j= yr.j'-'mon.j"-"dd.j                    /*reconstitute a date from above parts.*/
 end       /*j*/

between= abs( date('B', $.1, "I") - date('B', $.2, "I") ) /* # days between dates.*/ parse source . how . /*determine how invoked.*/ if how='COMMAND' then say commas(between) ' days between ' $.1 " and " $.2 exit between /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ commas: parse arg _; do c_=length(_)-3 to 1 by -3; _=insert(',', _, c_); end; return _ err: say; say '***error*** ' arg(1); exit 13 /*issue an error message (with text) */ isDec: return verify( arg(1), 1234567890) \== 0 /*insure argument is just decimal digs.*/ leapYr: arg _; ly=_//4==0; if ly==0 then return 0; ly=((_//100\==0)|_//400==0); return ly serDAT: call err 'illegal date format with a separator= ['sep"], date= " @dat /*──────────────────────────────────────────────────────────────────────────────────────*/ conv: parse arg @dat /*obtain date that the user specified. */ 

       if sep=='-'  then parse var  @dat    yr.a  "-"  mon.a  '-'  dd.a    /* yy-mm-dd */
       if sep=='/'  then parse var  @dat   mon.a  "/"   dd.a  '/'  yr.a    /* mm/dd/yy */
       if sep=='\'  then parse var  @dat    dd.a  "\"  mon.a  '\'  yr.a    /* dd\mm\yy */
       if yr.a==  then yr.a= right( date(), 4)                           /*omitted yy*/
       if length(yr.a)==2  then yr.a= left( date('S'), 2)yr.a              /*2 dig yy ?*/
       if yr.a==.  |  mon.a==.  |  dd.a==.  then call serDAT               /*validate. */
       return</lang>
output   when using the inputs of:     *   2000-1-1

Today   (indicated by the asterisk)   is   2019-10-2 

7,214  days between  2019-10-02  and  2000-01-01

Ring

<lang ring> load "stdlib.ring"

DaysBetween = [["1995-11-21","1995-11-21"], 

              ["2019-01-01","2019-01-02"],
              ["2019-01-02","2019-01-01"],
              ["2019-01-01","2019-03-01"],
              ["2020-01-01","2020-03-01"],
              ["1902-01-01","1968-12-25"],
              ["2090-01-01","2098-12-25"]]

for n = 1 to len(DaysBetween) 

   date1 = DaysBetween[n][1]
   date2 = DaysBetween[n][2]
   date3 = substr(date1,9,2) + "/" + substr(date1,6,2) + "/" + substr(date1,1,4)
   date4 = substr(date2,9,2) + "/" + substr(date2,6,2) + "/" + substr(date2,1,4)
   ? "Days between " + DaysBetween[n][1] + " and " + DaysBetween[n][2] + ": " + diffdays(date4,date3)

next </lang>

Output:
Days between 1995-11-21 and 1995-11-21: 0
Days between 2019-01-01 and 2019-01-02: 1
Days between 2019-01-02 and 2019-01-01: -1
Days between 2019-01-01 and 2019-03-01: 59
Days between 2020-01-01 and 2020-03-01: 60
Days between 1902-01-01 and 1968-12-25: 0
Days between 2090-01-01 and 2098-12-25: 3280

Ruby

<lang ruby>require "date"

d1, d2 = Date.parse("2019-1-1"), Date.parse("2019-10-19")

p (d1 - d2).to_i # => -291 p (d2 - d1).to_i # => 291 </lang>

Rust

<lang rust>// [dependencies] // chrono = "0.4"

use chrono::NaiveDate;

fn main() { 

   let args: Vec<String> = std::env::args().collect();
   if args.len() != 3 {
       eprintln!("usage: {} start-date end-date", args[0]);
       std::process::exit(1);
   }
   if let Ok(start_date) = NaiveDate::parse_from_str(&args[1], "%F") {
       if let Ok(end_date) = NaiveDate::parse_from_str(&args[2], "%F") {
           let d = end_date.signed_duration_since(start_date);
           println!("{}", d.num_days());
       } else {
           eprintln!("Can't parse end date");
           std::process::exit(1);
       }        
   } else {
       eprintln!("Can't parse start date");
       std::process::exit(1);
   }

}</lang>

Output:
days_between_dates 2020-01-01 2020-09-06
249

Scala

<lang scala>object DaysBetweenDates { 

 /*Inspired by the Python version of the algorithm and the discussion here
  https://stackoverflow.com/questions/12862226/the-implementation-of-calculating-the-number-of-days-between-2-dates.*/

 /**Transform a date into a day number in the Gregorian Calendar*/
 def dateToDays(year : Int, month : Int, day : Int ) : Int = {
   val m = (month+ 9) % 12
   val y = year - m/10
   val d = day
   365*y + y/4 - y/100 + y/400 + (m*306 + 5)/10 + (d - 1)
 }

 /**Compute the difference of days between both input dates*/
 def daysDifference(firstDate : String, secondDate : String) : Int = {
   val firstDateTuple = firstDate.split('-') match { case Array(a, b, c) => (a, b, c) }
   val secondDateTuple = secondDate.split('-') match { case Array(a, b, c) => (a, b, c) }

   val firstYear = dateToDays( firstDateTuple._1.toInt, firstDateTuple._2.toInt, firstDateTuple._3.toInt)
   val secondYear = dateToDays( secondDateTuple._1.toInt, secondDateTuple._2.toInt, secondDateTuple._3.toInt )

   return secondYear - firstYear
 }

 def main(args: Array[String]): Unit = {
   println(daysDifference("2019-01-01", "2019-09-30"))
   println(daysDifference("1995-11-21", "1995-11-21"))
   println(daysDifference("2019-01-01", "2019-01-02"))
   println(daysDifference("2019-01-02", "2019-01-01"))
   println(daysDifference("2019-01-01", "2019-03-01"))
   println(daysDifference("2020-01-01", "2020-03-01"))
   println(daysDifference("1902-01-01", "1968-12-25"))
   println(daysDifference("2090-01-01", "2098-12-25"))
   println(daysDifference("1902-01-01", "2098-12-25"))
 }

} </lang>

Output:
272
0
1
-1
59
60
24465
3280
71947

SenseTalk

SenseTalk supports date and time calculations in many forms, and many different units of time (such as 'days' in this example). Rounding is needed due to daylight savings time changes. <lang sensetalk>set startDate to "2020-03-13" set endDate to "2021-07-14"

put (endDate - startDate) rounded to nearest day </lang>

Output:
488 days

Sidef

<lang ruby>require('Date::Calc')

func days_diff(a,b) { 

   %S<Date::Calc>.Delta_Days(a.split('-')..., b.split('-')...)

}

var date1 = "1970-01-01" var date2 = "2019-10-02"

say "Date 1: #{date1}" say "Date 2: #{date2}"

var days = days_diff(date1, date2)

say "There are #{days} days between these dates"</lang>

Output:
Date 1: 1970-01-01
Date 2: 2019-10-02
There are 18171 days between these dates

Swift

<lang swift>import Foundation

func daysFromTimeInterval(_ interval: Double) -> Int { 

 return Int(interval) / 86400

}

let formatter = DateFormatter()

formatter.dateFormat = "yyyy-MM-dd"

print("Enter date one (yyyy-MM-dd): ", terminator: "")

guard let date1Str = readLine(strippingNewline: true), let date1 = formatter.date(from: date1Str) else { 

 fatalError("Invalid date two")

}

print("Enter date two (yyyy-MM-dd): ", terminator: "")

guard let date2Str = readLine(strippingNewline: true), let date2 = formatter.date(from: date2Str) else { 

 fatalError("Invalid date two")

}

let (start, end) = date1 > date2 ? (date2, date1) : (date1, date2) let days = daysFromTimeInterval(DateInterval(start: start, end: end).duration)

print("There are \(days) days between \(start) and \(end)")</lang>

Output:
Enter date one (yyyy-MM-dd): 2019-01-01
Enter date two (yyyy-MM-dd): 2019-12-02
There are 335 days between 2019-01-01 05:00:00 +0000 and 2019-12-02 05:00:00 +0000

UNIX Shell

Works with: Bourne Again Shell

<lang bash># return true if year is leap in Gregorian calendar leap() { 

 local -i year
 year=$1
 if (( year % 4 )); then return 1; fi
 if (( year % 100 )); then return 0; fi
 ! (( year % 400 ))

}

  1. convert date to Gregorian day count (Rata Die), where RD 1 = January 1, 1 CE

rd() { 

  local year month day
  IFS=- read year month day <<<"$1"
  local -i elapsed_years=year-1
  (( day += elapsed_years * 365 ))
  (( day += elapsed_years/4 ))
  (( day -= elapsed_years/100 ))
  (( day += elapsed_years/400 ))
  local month_lengths=(31 28 31 30 31 30 31 31 30 31 30 31)
  if leap "$year"; then let month_lengths[1]+=1; fi
  local m
  for (( m=0; m<month-1; ++m)); do
    (( day += month_lengths[m] ))
  done
  printf '%d\n' "$day"

}

days_between() { 

 local -i date1 date2
 date1=$(rd "$1")
 date2=$(rd "$2")
 printf '%d\n' $(( date2 - date1 ))

}

days_between 1970-01-01 2019-12-04 </lang>

Output:
18234

Visual Basic .NET

Translation of: C#

<lang vbnet>Imports System.Globalization

Module Module1 

   Function DateDiff(d1 As String, d2 As String) As Integer
       Dim a = DateTime.ParseExact(d1, "yyyy-MM-dd", CultureInfo.InvariantCulture)
       Dim b = DateTime.ParseExact(d2, "yyyy-MM-dd", CultureInfo.InvariantCulture)
       Return (b - a).TotalDays
   End Function

   Sub Main()
       Console.WriteLine(DateDiff("1970-01-01", "2019-10-18"))
   End Sub

End Module</lang>

Output:
18187

Wren

Library: Wren-date

<lang ecmascript>import "/date" for Date

var datePairs = [ 

   ["1995-11-21", "1995-11-21"],
   ["2019-01-01", "2019-01-02"],
   ["2019-01-02", "2019-01-01"],
   ["2019-01-01", "2019-03-01"],
   ["2020-01-01", "2020-03-01"],
   ["1902-01-01", "1968-12-25"],
   ["2090-01-01", "2098-12-25"],
   ["1902-01-01", "2098-12-25"],
   ["1970-01-01", "2019-10-18"],
   ["2019-03-29", "2029-03-29"],
   ["2020-02-29", "2020-03-01"]

] for (dates in datePairs) { 

   var date1 = Date.parse(dates[0])
   var date2 = Date.parse(dates[1])
   var days = (date2 - date1).days
   Date.default = Date.isoDate
   System.print("Days between %(date1) and %(date2) = %(days)")

}</lang>

Output:
Days between 1995-11-21 and 1995-11-21 = 0
Days between 2019-01-01 and 2019-01-02 = 1
Days between 2019-01-02 and 2019-01-01 = -1
Days between 2019-01-01 and 2019-03-01 = 59
Days between 2020-01-01 and 2020-03-01 = 60
Days between 1902-01-01 and 1968-12-25 = 24465
Days between 2090-01-01 and 2098-12-25 = 3280
Days between 1902-01-01 and 2098-12-25 = 71947
Days between 1970-01-01 and 2019-10-18 = 18187
Days between 2019-03-29 and 2029-03-29 = 3653
Days between 2020-02-29 and 2020-03-01 = 1

zkl

<lang zkl>var [const] TD=Time.Date; today:=TD.parseDate("--"); // "yyyy-mm-dd" and variations --> (y,m,d) // or Time.Clock.UTC --> (y,m,d,h,m,s) then:=TD.parseDate("2018-9-30"); diff:=TD.deltaDays(then,today.xplode()); // ( (y,m,d), y,m,d ) println("Number of days between %s and %s: %d".fmt(then,today,diff)); println("Number of days between %s and %s: %d".fmt( 

  TD.toYMDString(today.xplode()),	// to(y,m,d) not to((y,m,d))
  TD.toYMDString(then.xplode()),
  TD.deltaDays(today,then.xplode())));</lang>
Output:
Number of days between L(2018,9,30) and L(2019,9,30): 365
Number of days between 2019-09-30 and 2018-09-30: -365
Retrieved from "https://rosettacode.org/wiki/Days_between_dates?oldid=294312"