Days between dates

From Rosetta Code
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 & " -> " & 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

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

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

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

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

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.

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.

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

<lang Phix>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")</lang> 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]

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).

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. */ if $.1=='*' then $.1= date("I") /*obtain current date if it's an *. */ if $.2=='*' then $.2= date("I") /* " " " " " " " */ parse var $.1 yr.1 '-' mon.1 "-" dd.1 /*obtain the constituents of 1st date. */ parse var $.2 yr.2 '-' mon.2 "-" dd.2 /* " " " " 2nd " */ ?.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 the correct format: YYYY-MM-DD " 

 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*/

say commas(abs(date('B',$.1,"I") -date('B',$.2,"I"))) ' days between ' $.1 " and " $.2 exit /*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</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

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>

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

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

No built-in date support so we need to work from scratch. <lang javascript>var dayOfYear = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334]

var isLeapYear = Fn.new { |y| 

   return ((y % 4 == 0) && (y % 100!= 0)) || (y % 400 == 0)

}

// Parameters assumed to be in YYYY-MM-DD format. var daysBetween = Fn.new { |date1, date2| 

   date1 = date1.replace("-", "")
   date2 = date2.replace("-", "")
   var neg = false
   if (Num.fromString(date1) > Num.fromString(date2)) {
       var temp = date2
       date2 = date1
       date1 = temp
       neg = true
   }    
   var y1 = Num.fromString(date1[0..3])
   var m1 = Num.fromString(date1[4..5]) - 1
   var d1 = Num.fromString(date1[6..7])
   var y2 = Num.fromString(date2[0..3])
   var m2 = Num.fromString(date2[4..5]) - 1
   var d2 = Num.fromString(date2[6..7])
   var days = 0
   if (y1 == y2) {
       days = dayOfYear[m2] - dayOfYear[m1] + d2 - d1
       if (isLeapYear.call(y1) && m1 < 2 && m2 >= 2) days = days + 1
   } else {
       days = 365 - dayOfYear[m1] - d1
       if (isLeapYear.call(y1) && m1 < 2) days = days + 1
       days = days + dayOfYear[m2] + d2 
       if (isLeapYear.call(y2) && m2 > 1) days = days + 1
       if (y1 < y2 - 1) {
           for (y in y1+1..y2-1) {
               days = days + 365
               if (isLeapYear.call(y)) days = days + 1
           }
       }
   }
   return (neg) ? -days : days

}

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 days = daysBetween.call(dates[0], dates[1])
   System.print("Days between %(dates[0]) and %(dates[1]) = %(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=294288"