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CS 3723/3721  Programming Languages  Spring 2005  Recitation 14  Ruby: Basics, Classes and REs     Week 14: Apr 25-29  Due (on time): 2005-04-02  23:59:59  Due (late):        2005-04-06  23:59:59

Recitation 14 must be submitted following directions at: submissions with deadlines 2005-04-02  23:59:59 (that's Monday, 2 May 2005, 11:59:59 pm) for full credit. 2005-04-06  23:59:59 (that's Friday, 6 May 2005, 11:59:59 pm) for 75% credit.

Ruby: Basics, Classes and Regular Expressions:

Chapters to study:

• Ruby.new. Early overview chapter, Chapter 2 in the actual book (13 pages). (Study all of this except for "Hashes" and details of "Blocks and Iterators".)

• Classes, Objects, and Variables. The next chapter, Chapter 3 in the actual book (16 pages). (Skip the final third of this chapter, starting with "Singletons and Other Constructors" and then skip "Access Control" and "Variables".)

• Standard Types. Chapter 5 in the actual book (18 pages), the first half is easy and the second half deals with regular expressions. (Skip "Ranges" in the first half, and focus on the final subsection "Object-Oriented Regular Expressions" in the second half, without worrying about other details of regular expressions in the second half.)

You should also read and go over the examples in the:

• Online Tutorial. By the instructor.

1. Program involving regular expressions: Here are two forms for representing the time and date:

   "American" style	International style
   10:03pm April 20, 2004	2004-04-20 22:03:00
   8:04am January 4, 1998	1998-01-04 08:04:00
   11:59pm December 31, 2003	2003-12-31 23:59:59
   0:00am January 1, 2000	2000-01-01 00:00:00

   1. Write a Ruby program that translates International style dates to "American" style dates:
      1. Read a sequence of International style dates, one to a line, and translate these into the American style.
      2. Use Ruby regular expressions as an essential part of the program. (Follow the model of the regular expression program at the end of the Ruby tutorial.) You must not use the Perl-like variables $1, $2, etc., but must program this using Ruby's object-oriented features.
      3. To help with the translation, use a Ruby array with the names of the twelve months in it.
      4. Notice that in the first sample date above, the hour of "22" must be changed to a "10" with "pm" at the end. Notice also that in the second sample date above, the "08" for hours and the "04" for days must be written in American style without the leading "0".
      5. Notice that the "American"style leaves off the seconds. You can leave them off also, or put them in if you wish.
      6. Do not check for input errors.

   2. Write a similar program that will translate from American style to International style. (This is similar code, but perhaps a little harder. Assume some reasonable definition for the "American" style, as shown above. If you leave seconds off in the "Ameican" style, you should put :00 back into the International style.)

      In addition to methods to_i (to int) and to_s (to string), You might find the following functions helpful:

      Functions pad0 and strip0
      #!/usr/local/bin/ruby def pad0(t) # if t as an integer is < 10, add 0 at left if t.to_i < 10 "0" + t else t end end def strip0(t) # remove 0 at left of input string t (if present) if t =~ /^0/ t[1,t.length-1] else t end end print pad0("9"), "\n" # prints 09 print pad0("19"), "\n" # prints 19 print strip0("03"), "\n" # prints 3 print strip0("23"), "\n" # prints 23

2. Program involving classes:

   Note that even though this problem also involves dates, it is independent of the previous problem -- you should not have any common code between the two problems. This problem has you working with dates and times. Ruby, like most programming languages, has library functions for treating times and dates, and in normal applications, you should use such library functions. This problem has you creating classes from scratch in order to learn how to do it.

   Consider the following Date class in Ruby. (Here is the whole file, Date class plus test code: date.rb.)

   Date class in Ruby, file: date.rb
   The class Date	Test code and a run
   #!/usr/local/bin/ruby class Date attr_reader :year, :month, :day def initialize(y, m, d) if check_date(y, m, d) @year, @month, @day = y, m, d else @year, @month, @day = 2000, 1, 1 end end @@mon = [nil,"Jan","Feb","Mar","Apr", "May","Jun","Jul","Aug", "Sep","Oct","Nov","Dec"] @@days = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31] def check_date(y, m, d) if m < 1 or m > 12 or d < 0 or d > 31 or y < 0 false elsif d > 0 and d <= @@days[m] true elsif m == 2 and d == 29 and is_leap(y) true else false end end def is_leap(y) if (y%400 == 0 or (y%4 == 0 and y%100 != 0) ) true else false end end def to_s @@mon[@month] + " " + day.to_s + ", " + year.to_s end def incr_day @day +=1 if not (@month == 2 and is_leap(@year) and @day == 29) and @day > @@days[@month] @day = 1 incr_month end end def incr_month @month +=1 if @month > 12 @month = 1 incr_year end end def incr_year @year += 1 end end	def test_date(y, m, d) date = Date.new(y, m, d) print "Start Date: ",date," " date.incr_day print "\n Next day: ", date date.incr_day print "\n Next day: ", date date.incr_day print "\n Next day: ", date, "\n" end test_date(2004, 4, 22) test_date(2000, 2, 28) test_date(2001, 2, 27) test_date(2001, 12, 30) % date.rb Start Date: Apr 22, 2004 Next day: Apr 23, 2004 Next day: Apr 24, 2004 Next day: Apr 25, 2004 Start Date: Feb 28, 2000 Next day: Feb 29, 2000 Next day: Mar 1, 2000 Next day: Mar 2, 2000 Start Date: Feb 27, 2001 Next day: Feb 28, 2001 Next day: Mar 1, 2001 Next day: Mar 2, 2001 Start Date: Dec 30, 2001 Next day: Dec 31, 2001 Next day: Jan 1, 2002 Next day: Jan 2, 2002

   1. In the same file add another class Time that will keep track of hours, minutes, and seconds. This new class should be similar to the Date class. In particular, it should have methods: initialize, check_time, to_s, incr_sec, incr_min, and incr_hour. Test this new class with code to instantiate time objects and to test incrementing by seconds, including showing that it handles the end of a minute and the end of an hour correctly.

   2. Change your Time class so that it inherits the Date class, that is Date is a superclass of Time, and Time is a subclass of Date. (In Java terms, Time extends Date, and in place of the Java "Time extends Date", Perl writes "Time < Date". The initializer for Time should now have 6 parameters, including the ones before, along with year, month, and day. These last three will be passed on into Date using the super method. (See the example KaraokeSong in Chapter 3 of the PPG.)

   3. Alter the incr_hour method of Time, so that in case an addition goes past hour 23, it will wrap around to hour 0 and increment to the next day.

      It is permissible to change the code in the class Date, although I didn't need to make any changes. There are many different ways to write this code. You should test your program with the following initial data, and your output should look something like the following:

      Possible output for this question

      Start Time: Apr 22, 2004 13:15:30 Next second: Apr 22, 2004 13:15:31 Next second: Apr 22, 2004 13:15:32 Start Time: Feb 28, 2000 13:59:59 Next second: Feb 28, 2000 14:00:00 Next second: Feb 28, 2000 14:00:01 Start Time: Feb 28, 2000 23:59:59 Next second: Feb 29, 2000 00:00:00 Next second: Feb 29, 2000 00:00:01 Start Time: Feb 29, 2000 23:59:59 Next second: Mar 1, 2000 00:00:00 Next second: Mar 1, 2000 00:00:01 Start Time: Feb 28, 2001 23:59:59 Next second: Mar 1, 2001 00:00:00 Next second: Mar 1, 2001 00:00:01 Start Time: Dec 31, 2001 23:59:58 Next second: Dec 31, 2001 23:59:59 Next second: Jan 1, 2002 00:00:00 Start Time: Apr 30, 2001 23:59:58 Next second: Apr 30, 2001 23:59:59 Next second: May 1, 2001 00:00:00

Contents of submission for Recitation 14: Last Name, First Name; Course Number; Recitation Number. 1. For full credit, you might have two Ruby programs that will translate in each direction. You should test each program at least with the four examples shown in the write-up above. However, you can also put everything into one program, which is what I did, producing two functions, one for each of the translations. (The true American style would write the fourth input above (midnight) in the form 12:00am January 1, 2000, and you could fix your program up to do this also.) 2. For part credit, you might just create the class Time. As a completely separate class, this is very similar to Date, but simpler, so you should really try this one. Parts ii and iii just add extra features. For full credit, it is enough to have a single Ruby program in a single file that does everything, producing roughly the output shown above for the 7 given inputs. (Of course, the two classes could also be in separate files.)