feat: add code

.gitignore

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+*.swp
+.DS_Store
+bin/configlet
+bin/configlet.exe
+temp.pl

.vscode/extensions.json

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+{
+    "recommendations": [
+        "rebornix.prolog"
+    ]
+}

code/main.pl

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+% month_days(Month, DaysInMonth, DaysBeforeMonth) 
+% returns the number of days in Month and the number of days it takes to reach that date in year 2023
+% prolog works by defining facts and rules and when queried about them returns values
+% it works different from functional programming in this  aspect since it doesn't just follow instruction it returns output based on world state
+month_days('01', 31, 0).
+month_days('02', 28, 31).
+month_days('03', 31, 59).
+month_days('04', 30, 90).
+month_days('05', 31, 120).
+month_days('06', 30, 151).
+month_days('07', 31, 181).
+month_days('08', 31, 212).
+month_days('09', 30, 243).
+month_days('10', 31, 273).
+month_days('11', 30, 304).
+month_days('12', 31, 334).
+
+% day_of_year(Date, DayOfYear) converts a date to day of year number later used to calculate interval
+% It also checks if number of days given by user is smaller or equal to number of days in the given month and if no then it gives fail
+day_of_year(Date, DayOfYear) :-
+  atom_chars(Date, Chars),
+  append(DayChars, MonthChars, Chars),
+  atom_chars(Day, DayChars),
+  atom_chars(Month, MonthChars),
+  month_days(Month, DaysInMonth, MonthDays),
+  atom_number(Day, DayNumber),
+  (DayNumber > DaysInMonth -> fail ; DayOfYear is MonthDays + DayNumber).
+
+% interval(Date1, Date2) prints the number of days between Date1 and Date2
+% We always expect date to be in format ddmm where 'd' stands for day and 'm' stands for month
+% if the month or day is just a single digit we expecte there to be zero in front 
+% (like 0505 for 5th of may or 1105 for 11th of may or 0511 for 5th of november)
+% write(Interval) prints out result, nl writes newline to make output conform to project requirements as much as possible
+interval(Date1, Date2) :-
+  (day_of_year(Date1, DayOfYear1), day_of_year(Date2, DayOfYear2) ->
+    Interval is abs(DayOfYear2 - DayOfYear1),
+    write(Interval), nl
+  ;
+    write('Invalid input.'), nl, fail
+  ).