---

« cheap cialis

buy xanax »

November 16th, 2006

, A short time ago in a galaxy not so far, , far away I came across a nice blog post: 15 Exercises for Learning a new Programming Language.

, One could argue if these are *really* the most appropriate 15(+) exercises to learn a new programming language - however, , the task of answering this rather complex question is left as an exercise for the reader. , Instead of this I will show you their implementation in Ruby - rubyrailways.com style.

, Why did I bother to solve these problems (including not really trivial ones, , like a scientific calculator with a GUI) ? Well, , actually to learn a new programming language! I still consider myself a beginner Ruby apprentice just playing it by ear in my somewhat scarce free time, , so I thought that systematically implementing a task list like this will mean great step forward for me compared to just coding random things at random times. , Fortunately I was perfectly right!

, Before we move onto the code, , one last disclaimer: the fact that I am still a Ruby n00b implies that the code can be somewhat hairy/not optimal/[insert any other language than Ruby here]-ish so don’t use these snippets as a textbook solution of the problems or anything like that. , I would be glad if someone could suggest a bit of refactoring of the bad parts but I also hope that that there are some nice parts which you can learn from (actually I am quite sure about this since I used some magick formulas from a few Ruby (grand)masters in some cases).

, OK, , enough talk for now. , Let’s see the stuff!

, 1. , Problem: “Display series of numbers (1, ,2, ,3, ,4, , 5….etc) in an infinite loop. , The program should quit if someone hits a specific key (Say ESCAPE key).”

, Solution: Hmm, , well, , errr…uh-oh… , I could not solve this problem fully (what a terrific start :-)). , If Henry Ford would sit beside me now, , he would say : You can hit any key to exit - so long as it’s ‘C’ - and one more advice: don’t forget to hold CTRL during this action :-). , More on this after the code snippet:

,

i = 0
loop { print "#{i+=1}, , " }

1. i = 0
2. loop { print "#{i+=1}, , " }

, Comments : If anyone knows how to add code which will cause this program to stop with a specific keyhit (say ‘ESC’) please, , please, , please drop me a note. , I have been researching this for at least 10% of the time of solving all the tasks, , nearly spitting blood when I gave up :-). , It seems (to me) that there is no simple (i.e. , no threads and similar) and clean platform-independent solution for this problem. , I guess (hope) the author’s idea here was different than to introduce threading or writing platform specific-code…

, 2. , Problem: “Fibonacci series, , swapping two variables, , finding maximum/minimum among a list of numbers.”

, Solution:

,

#Fibonacci series
Fib = Hash.new{ |h, , n| n < 2 ? h[n] = n : h[n] = h[n - 1] + h[n - 2] }
puts Fib[50]

#Swapping two variables
x, ,y = y, ,x

#Finding maximum/minimum among a list of numbers
puts [1, ,2, ,3, ,4, ,5, ,6].max
puts [7, ,8, ,9, ,10, ,11].min

1. #Fibonacci series
2. Fib = Hash.new{ |h, , n| n < 2 ? h[n] = n : h[n] = h[n - 1] + h[n - 2] }
3. puts Fib[50]
4.  
5. #Swapping two variables
6. x, ,y = y, ,x
7.  
8. #Finding maximum/minimum among a list of numbers
9. puts [1, ,2, ,3, ,4, ,5, ,6].max
10. puts [7, ,8, ,9, ,10, ,11].min

, Comments: The Fibonacci code was written by Andrew Johnson (found via Ruby Quiz). , I like it so much that I think it would be a shame to present a trivial version here. , I guess the rest of the code is self-explanatory.

, 3. , Problem: “Accepting series of numbers, , strings from keyboard and sorting them ascending, , descending order.”

, Solution:

,

a = []
loop { break if (c = gets.chomp) == 'q'; a << c }
p a.sort
p a.sort { |a, ,b| b<=>a }

1. a = []
2. loop { break if (c = gets.chomp) == ‘q’; a << c }
3. p a.sort
4. p a.sort { |a, ,b| b<=>a }

, Comments: This version is accepting strings - I think anybody who got to this point can adapt it to work with numbers. ,

, 4. , Problem: “Reynolds number is calculated using formula (D*v*rho)/mu Where D = Diameter, , V= velocity, , rho = density mu = viscosity Write a program that will accept all values in appropriate units (Don’t worry about unit conversion) If number is < 2100, , display Laminar flow, , If it’s between 2100 and 4000 display 'Transient flow' and if more than '4000', , display 'Turbulent Flow' (If, , else, , then...)"

, Solution:

,

vars = %w{D V Rho Mu}

vars.each do |var|
  print "#{var} = "
  val = gets
  eval("#{var}=#{val.chomp}")
end

reynolds = (D*V*Rho)/Mu.to_f

if (reynolds < 2100)
  puts "Laminar Flow"
elsif (reynolds > 4000)
  puts "Turbulent Flow"
else
  puts "Transient Flow"
end

1. vars = %w{D V Rho Mu}
2.  
3. vars.each do |var|
4.   print "#{var} = "
5.   val = gets
6.   eval("#{var}=#{val.chomp}")
7. end
8.  
9. reynolds = (D*V*Rho)/Mu.to_f
10.  
11. if (reynolds < 2100)
12.   puts "Laminar Flow"
13. elsif (reynolds > 4000)
14.   puts "Turbulent Flow"
15. else
16.   puts "Transient Flow"
17. end

, Comments: Can you spot the trick in the part which is filling up the variables? They don’t go out of scope after the loop ends because they are constants. , Other possibility would be to use $global variables but I guess it is usually not a very good programming practice to do that.

, 5. , Problem: “Modify the above program such that it will ask for ‘Do you want to calculate again (y/n), , if you say ‘y’, , it’ll again ask the parameters. , If ‘n’, , it’ll exit. , (Do while loop) While running the program give value mu = 0. , See what happens. , Does it give ‘DIVIDE BY ZERO’ error? Does it give ‘Segmentation fault..core dump?’. , How to handle this situation. , Is there something built in the language itself? (Exception Handling)”

, Solution:

,

vars = { "d" => nil, , "v" => nil, , "rho" => nil, , "mu" => nil }

begin
  vars.keys.each do |var|
    print "#{var} = "
    val = gets
    vars[var] = val.chomp.to_i
  end

  reynolds = (vars["d"]*vars["v"]*vars["rho"]) / vars["mu"].to_f
  puts reynolds

  if (reynolds < 2100)
    puts "Laminar Flow"
  elsif (reynolds > 4000)
    puts "Turbulent Flow"
  else
    puts "Transient Flow"
  end

  print "Do you want to calculate again (y/n)? "
end while gets.chomp != "n"

1. vars = { "d" => nil, , "v" => nil, , "rho" => nil, , "mu" => nil }
2.  
3. begin
4.   vars.keys.each do |var|
5.     print "#{var} = "
6.     val = gets
7.     vars[var] = val.chomp.to_i
8.   end
9.  
10.   reynolds = (vars["d"]*vars["v"]*vars["rho"]) / vars["mu"].to_f
11.   puts reynolds
12.  
13.   if (reynolds < 2100)
14.     puts "Laminar Flow"
15.   elsif (reynolds > 4000)
16.     puts "Turbulent Flow"
17.   else
18.     puts "Transient Flow"
19.   end
20.  
21.   print "Do you want to calculate again (y/n)? "
22. end while gets.chomp != "n"

, Comments: As you can see, , I could not use the same trick here when asking for the variables, , because when somebody wants to calculate again, , Ruby will complain (although by printing a warning only) that the constants have been already set up. , Therefore I went for the hash solution. , I think the do-you-want-to-calculate-again part is straightforward so I won’t analyze that here.
“While running the program give value mu = 0.”
Ruby gives a rather interesting result in this case: infinity :-).
“Is there something built in the language itself?”
Sure: exception handling. , Division by zero could be caught with a ZeroDivisionError rescue clause.

, 6. , Problem: “Scientific calculator supporting addition, , subtraction, , multiplication, , division, , square-root, , square, , cube, , sin, , cos, , tan, , Factorial, , inverse, , modulus”

, Solution:
Since this code snippet is longer It would look ugly here - you can download it from here instead. ,

Screenshot:

, If you would like to try it, , you will need the Tk bindings for Ruby (maybe you have them already, , here on Ubuntu I did not). , Also note that only the regular 0-9 keys (and of course the mouse) work, , the numpad ones do not. , One more little detail: % stands for modulo, , not percent.

, Comments: Phew, , this was a real challenge, , mostly because I never did any GUI in Ruby before. , I was amazed that I could code up a relatively feature rich calculator in 100+ lines of code, , without any golfing or trying to optimize for shortness. , What I wanted to say with this is that the shortness does not praise my programming skills (since I did not eve try to golf) but the superb terseness of Ruby. , OK, , of course there are some problems (e.g. , cube, , cos, , tan, , inverse are not implemented) but the usability/amount of code ratio is unbelievably high.

, The GUI is also not the nicest since I have used Tk - wxRuby or qt-ruby would produce much nicer results, , but since I did not code any GUI in Ruby previously, , I have decided to try the good-old-skool Tk for the first time.

, 7. , Problem: “Printing output in different formats (say rounding up to 5 decimal places, , truncating after 4 decimal places, , padding zeros to the right and left, , right and left justification)(Input output operations)”

, Solution:

,

#rounding up to 5 decimal pleaces
puts sprintf("%.5f", , 124.567896)

#truncating after 4 decimal places
def truncate(number, , places)
  (number * (10 ** places)).floor / (10 ** places).to_f
end

puts truncate(124.56789, , 4)

#padding zeroes to the left
puts 'hello'.rjust(10, ,'0')

#padding zeroes to the right
puts 'hello'.ljust(10, ,'0')

#right justification
puts ">>#{'hello'.rjust(20)}<<"

#left justification
puts ">>#{'hello'.ljust(20)}<<"

1. #rounding up to 5 decimal pleaces
2. puts sprintf("%.5f", , 124.567896)
3.  
4. #truncating after 4 decimal places
5. def truncate(number, , places)
6.   (number * (10 ** places)).floor / (10 ** places).to_f
7. end
8.  
9. puts truncate(124.56789, , 4)
10.  
11. #padding zeroes to the left
12. puts ‘hello’.rjust(10, ,’0‘)
13.  
14. #padding zeroes to the right
15. puts ‘hello’.ljust(10, ,’0‘)
16.  
17. #right justification
18. puts ">>#{’hello’.rjust(20)}<<"
19.  
20. #left justification
21. puts ">>#{’hello’.ljust(20)}<<"

, Comments: Amazingly lot of things can be done with sprintf() - I could solve nearly all the problems with it - but that would not really be rubyish, , so I have decided for built-in (and one homegrown) functions. , However, , mastering (s)printf() is a very handy thing, , since nearly all big players (C (of course :-)), , C++, , Java, , PHP, , … , ) have it so you get a powerful function in more languages for the price of learning one). , As you can see, , r/ljust is a nice one, , too.

, 8. , Problem: “Open a text file and convert it into HTML file. , (File operations/Strings)”

, Solution: Well, , this problem was not specified in a great detail, , to say the least - or to put it otherwise, , the solvers are given a great freedom to provide a solution spiced up with their fantasy. , This is what I came up with:

,

doc = <, Nothing really interesting here, , just plain text.

This is the second paragraph. , Let's see some *strong* markup in action, , and also /italic/. , So far soo good.

This is the last paragraph, , with one more strong tag.
DOC

final_doc = <
  
    
  
  
    
, 
    embed_doc_here
    
  

, "} final_doc.sub!(/embed_doc_here/) {doc} puts final_doc

, Comments: As you can see, , besides that the text is wrapped around with a minimal HTML, , every occurrence of words between asterisks is outputted in strong and between slashes in italic. , You can add as many such rules as you like, , they will be (hopefully) substituted in the final output.

, 9. , Problem: “Time and Date : Get system time and convert it in different formats ‘DD-MON-YYYY’, , ‘mm-dd-yyyy’, , ‘dd/mm/yy’ etc.”

, Solution: Well, , it was not really clear (for me) what should be the difference between ‘yyyy’ and ‘YYYY’ (resp. , ‘dd’ vs ‘DD’) so again I had to use my imagination. , However, , I guess it does not matter too much, , the solution has to be changed by 1-2 characters only if the original author had something different on his mind.

,

require 'date'

time = Time.now
#'DD-MON-YYYY', , e.g. , 12-Nov-2006 in my interpetation
puts time.strftime("%d-%b-%Y")

#'mm-dd-yyyy', , e.g. , 11-12-2006 in my interpetation
puts time.strftime("%m-%d-%Y")

#'dd/mm/yy', , e.g. , 12/11/2006 in my interpetation
puts time.strftime("%d/%m/%Y")

, 10. , Problem: “Create files with date and time stamp appended to the name”

, Solution:

,

#Create files with date and time stamp appended to the name
require 'date'

def file_with_timestamp(name)
  t = Time.now
  open("#{name}-#{t.strftime('%m.%d')}-#{t.strftime('%H.%M')}", , 'w')
end

my_file = file_with_timestamp('test.txt')
my_file.write('This is a test!')
my_file.close

, Comments: Maybe a more elegant solution could be to subclass File and override its constructor - but maybe that would be an overkill. , I have voted for the latter option in this case :-).

, 11. , Problem: “Input is HTML table. , Remove all tags and put data in a comma/tab separated file.”

, Solution: Since web extraction is both my PhD topic and my everyday job (and even my free-time activity :-)) I will present 3 solutions for this problem. , First, , the classic old-school regexp way (by Paul Lutus), , then with HPricot and finally with scRUBYt!, , a simple yet powerful Ruby web extraction framework currently developed by me.

,

table = <
  
    1
    2
  
  
    3
    4
    5
  
  
    6
  

DOC

rows = table.scan(%r{.*?}m)

rows.each do |row|
   fields = row.scan(%r{(.*?)}m)
   puts fields.join(", ,")
end

, Now for the HPricot solution (in the further examples let’s consider that table is initialized as in the previous example):

require 'rubygems'
require 'hpricot'

h_table = Hpricot(table)

rows = h_table/"//tr"
rows.each do |row|
  child_text = (row/"//td").collect {|elem| elem.innerHTML }
  puts child_text.join(', ,')
end

, and last, , but not least scRUBYt!

require 'scrubyt'

table_data = P.table do
               P.cell '1'
             end

table_data.generalize :cell

puts table_data.to_csv

, Some explanation: first of all, , at the moment scRUBYt! is avaliable on my hard disk (and partially in my head) only - it should be released around XMAS 2006. , I am using this solution for a little bit of self-promotion :-). ,

, The example works like this: extract something (in this case a HTML <table>) which has something (in this case <td>) which has ‘1′ as its text (well in reality much more is going on in the background, , but roughly along these lines). , This little code snippet will extract the first <td>s of ALL <tables> on a HTML page. , With the ‘generalize’ call we tell the extractor that it should not extract just the first <td> in a table (which is the default setting), , but all of them.

, scRUBYt! can handle much, , much, , MUCH more complicated examples than this (like an ebay or amazon page) and has loads of sophisticated functions… , so stay tuned!

, 12. , Problem: “Extract uppercase words from a file, , extract unique words.”

, Solution: (you can find some_uppercase_words.txt here and some_repeating_words.txt here

,

open('some_uppercase_words.txt').read.split().each { |word| puts word if word =~ /^[A-Z]+$/ }

words = open('some_repeating_words.txt').read.split()
histogram = words.inject(Hash.new(0)) { |hash, , x| hash[x] += 1; hash}
histogram.each { |k, ,v| puts k if v == 1 }

, 13. , Problem: “Implement word wrapping feature (Observe how word wrap works in windows ‘notepad’).”

, Solution: Unfortunately I am not a Windows user and I have seen notepad a *quite* long time ago - so I am not sure the task and it’s implementation are fully in-line - I have tried my best. , Here we go:

,

input = "Lorem ipsum dolor sit amet, , consectetur adipisicing elit, , sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. , Ut enim ad minim veniam, , quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. , Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. , Excepteur sint occaecat cupidatat non proident, , sunt in culpa qui officia deserunt mollit anim id est laborum."

def wrap(s, , len)
  result = ''
  line_length = 0
  s.split.each do |word|
    if line_length + word.length + 1  < len
      line_length += word.length + 1
      result += (word + ' ')
    else
      result += "\n"
      line_length = 0
    end
  end
  result
end

puts wrap(input, , 30)

, 14. , Problem: “Adding/removing items in the beginning, , middle and end of the array.”

, Solution:

,

x = [1, ,3]

#adding to beginning
x.unshift(0)

#adding to the end
x << 4

#adding to the middle
x.insert(2, ,2)

#removing from the beginning
x.shift

#removing from the end
x.pop

#removing from the middle
x.delete(2)

#we have arrived at the original array!

, 15. , Problem: “Are these features supported by your language: Operator overloading, , virtual functions, , references, , pointers etc.”

, Solution: Well this is not a real problem (not in Ruby, , at least). , Ruby is a very high level language ant these things are a must :).

Finally, , you can download all the solutions in a single archive from here. I would like to see the implementation of these tasks in both Ruby (different (more optimal) solutions of course) as well as in anything else. , If you set out to do something like that, , be sure to drop me a note.

Similar Posts:prozac

If you liked the article, subscribe to the feed   and follow me on .

This entry was posted on Thursday, November 16th, 2006 at 4:31 am and is filed under Devel, Ruby, Tutorial. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

31 Responses to “”

1. Jamie Macey Says:
   November 16th, 2006 at 11:36 am

   , The “break calculation at a keypress” is as follows - essentially just do a nonblocking read and rescue the “resource not available” exceptions as they come. Just hit enter to kill the loop.

   , i=0
   loop do
   begin
   break if STDIN.read_nonblock(1000)
   rescue Errno::EAGAIN
   end
   puts i
   i += 1
   end

   , For #4, , I’d recommend using @instance variables. Use instancevariableset instead of eval. Eval is very dangerous, , especially when you’re not checking it like there. Storing it in a hash like you have for #5 is good as well.

   , For #8, , the redcloth and bluecloth (textile and markdown, , respectively) are dead-simple html converters.

2. Satish Talim Says:
   November 16th, 2006 at 9:39 pm

   , I liked this post of yours and have requested the readers of my Learning Ruby site to contribute their thoughts etc. to this post.
   http://sitekreator.com/satishtalim/ruby_certification.html

3. peter Says:
   November 17th, 2006 at 12:31 am

   , Jamie:

   , Thanks for the reply!
   I have modified your code a bit:

   require 'io/nonblock'
   
   i=0
   loop do
     begin
       break if STDIN.nonblock{ STDIN.sysread(100) }
     rescue Errno::EAGAIN
     end
     puts i += 1
   end
   

   , Which is cool - but there is one problem: You need Henry Ford again :-). The original task was to stop on a specified key, , say ‘ESC’ or ‘x’ (and no enter afterwards) and this code stops solely on enter. Can it be modified to stop on ‘esc’?

   , As for the eval - tanks for the suggestion. For #4, , I wanted to write the shortest code possible for better understanding. While #5 is more secure and this is how it should like in a real-life app, , I think it is also harder to comprehend for a beginner. But anyway, , the moral of the story is that we should not use eval too much

   , RedCloth/BlueCloth - I will check them out and ad them to the solution.

4. peter Says:
   November 17th, 2006 at 12:34 am

   , Satish:

   , Cool! I hope a conversation, , beneficial for both parties, , will be started :-). There are tons of other ways to code these examples and I would like to hear other ideas as well. Thanks.

5. Subbu Says:
   November 17th, 2006 at 4:45 am

   , Hey i had no clue about Ruby until this morning.But think i am falling in love with it..your codes were really helpful for me to have a look at how basic ruby programming will be…
   a single glitch :
   the link in the problem No:6 to download the code for it is not proper.It redirects to the same page.

6. peter Says:
   November 18th, 2006 at 1:27 am

   , Subbu, ,

   , Thanks for the ‘bug report’. It should be corrected by now.

7. Ruby, Rails, Web2.0 » Blog Archive » Site Updates Says:
   December 6th, 2006 at 4:23 am

   , [...] « Implementing ‘15 Exercises for Learning a new Programming Language’ [...]

8. Ken Laninga Says:
   December 10th, 2006 at 2:53 pm

   , Hello, , (?????) I don’t think I saw your name………. sorry if I’m blind…….

   , Just heard about Ruby yesterday and it looks fascinating. I programmed a lot in QuickBasic loooooong ago but Win95 put me out of that business.

   , Everybody shows bits of Ruby code, , but nobody starts far enough back to tell me HOW to do that; do I just type the code in Notepad or Wordpad and then save it as abcd.exe and run it? (or compile it into .exe first)

   , Can we start at “square one” please? Some of us are n00bs.

9. peter Says:
   December 11th, 2006 at 3:33 am

   , Hi Ken, ,

   , My name is Peter (if you go to https://rubyrailways.com, , there is a ‘whoami’ link on the right)… It’s kinda linux-style so it may look weird to some non-*nix guys

   , QuickBasic was cool… I also used to program a lot in it (after I got my first PC - before that I had a Sinclair ZX Spectrum and a Commodore 64, , so those were my first BASICs but ruby is much, , much cooler…

   , As for the HOWTO part: Ruby is (like BASIC) an intepreted language - this means that the code is not compiled to a binary format (though it is posible to do so) but interpreted on the fly. So you enter the stuff into notepad, , then save the file as ‘mycoolprogram.rb’ and either type

   ruby my_cool_program.rb
   

   , to a commadline shell, , or set up a file association on the type ‘.rb’ and just double click it (however, , some further tweaking may be needed here , , since if I remember correctly a shell pops up with the output then it closes immediately so you can not inspect the output).

   , First you should install Ruby: Check out this page: http://rubyinstaller.rubyforge.org/

   , Then you should make sure that ruby is in the path… and this should be about it.

   , If you still have questions, , don’t hesitate to write me (at peter@[name of this site].com). The Ruby mailing list is also a good place to start, , no matter how noob or expert you are - the people are really helpful.

   , Hope this helps…

10. Robert Says:
    December 27th, 2006 at 3:07 am

    , Great read. It shows a lot of the ways that Ruby establishes itself from the other languages. My only real comment is that on problem 5. The question says “if you say ‘y’, , it’ll again ask the parameters. If ‘n’, , it’ll exit”. The way you have it implemented is so that anything other than ‘n’ will continue the loop. It wouldn’t be a bad idea to throw in a method that check for y/n and if gets is !y/n then shout out some type of “Invalid char.” nonsense and have it re-loop the y/n question. This isn’t really an issue with the programming, , just a statement to those confused by why when they accidentally hit ‘/[^n]/’ on their keyboard. All in all, , I think it is great that you put this up. Now, , if others would just make more like yours but in different languages.

11. botp Says:
    January 26th, 2007 at 11:47 pm

    , Hi Peter, ,

    , very nice blog.
    as for problem #1, , you can do something like the ff (in windows), ,

    , C:\family\ruby\key_press>cat a1b.rb

    ---

    , require ‘Win32API’

    , @@kbhit = Win32API.new(”msvcrt”, , “kbhit”, , [], , ‘I’)
    @@getch = Win32API.new(”msvcrt”, , “getch”, , [], , ‘I’)

    , def exit_onkey key
    unless @@kbhit.call.zero?
    c = @@getch.call
    if c == key
    exit
    end
    end
    end

    , KEY_Esc = 27
    $stdout.sync=true

    , i=0
    loop do
    exitonkey KEYEsc
    puts “#{i+=1}”
    end

    ---

    , note, , that we created another method exit_onkey just for readability and flexibility purposes.
    kind regards -botp

12. Satish Talim Says:
    March 14th, 2007 at 11:06 pm

    , Anyone here has used ncurses for problem no. 1?

13. links for 2007-05-23 « mriror Says:
    May 22nd, 2007 at 11:55 pm

    , [...] Ruby, , Rails, , Web2.0 » Blog Archive » Implementing ‘15 Exercises for Learning a new Programming Language’ [...]

14. bshand Says:
    July 17th, 2007 at 4:02 am

    , In lines 11-12 of example 13, , I think you mean:
    result += “\n” + word + ‘ ‘
    linelength = word.length + 1
    instead of
    result += “\n”
    linelength = 0
    otherwise the words that trigger line breaks are lost.
    Or, , with slightly less repetition:
    s.split.each do |word|
    if linelength + word.length + 1 >= len
    result += “\n”
    linelength = 0
    end
    line_length += word.length + 1
    result += (word + ‘ ‘)
    end

15. Jakob Says:
    July 29th, 2007 at 12:08 am

    , This is exactly what I expected to find out after reading the title . Thanks for informative article

16. links for 2007-08-23 « Bloggitation Says:
    August 22nd, 2007 at 5:19 pm

    , [...] Implementing 15 Exercises for Learning a new Programming Language’ implement them in your favorite language (tags: ruby programming blog) [...]

17. Hotels Vlaanderen Says:
    August 29th, 2007 at 7:38 am

    , Great blog !

18. wurzel Says:
    October 28th, 2007 at 1:06 pm

    , I cant get the break on ENTER loop working on ruby 1.8.6

    , require ‘io/nonblock’

    , i=0
    loop do
    begin
    break if STDIN.nonblock{ STDIN.sysread(100) }
    rescue Errno::EAGAIN
    end
    puts i += 1
    end

    , any ideas why?

    , I get this error

    , loopESC.rb:6: undefined method nonblock' for #<IO:0x2846b04> (NoMethodError)
from loopESC.rb:4:inloop’
    from loopESC.rb:4

19. Figet Says:
    December 18th, 2007 at 7:32 am

    , Nice blog!

20. knownone Says:
    January 13th, 2008 at 8:56 am

    , are your platform windows?nonblock.rb requires fcntl, ,but it didn’t implement on all platforms?

21. James Edward Gray II Says:
    January 17th, 2008 at 6:54 am

    , I see there’s already a Windows specific answer to the first problem, , so I shall provide the Unix solution:

    #!/usr/bin/env ruby -wKU
    
    require "io/wait"
    
    state = `stty -g`
    begin
      system "stty raw -echo cbreak isig"
    
      1.upto(1.0/0.0) do |n|
        puts n
        exit if $stdin.ready? and $stdin.getc == 27
      end
    
    ensure
      system "stty #{state}"
    end
    
    __END__
    

    , The reason you need the platform specific code here is that you are doing complex interactions (reading and writing at the same time) with a terminal and all terminals are different.

22. Vince Says:
    January 24th, 2008 at 7:20 pm

    , In solution #3 instead of << p a.sort { |a, ,b| b<=>a } >> you could use << p a.sort.reverse >>…just more readable

23. Diesel Says:
    March 15th, 2008 at 6:43 am

    ,

24. Bill Says:
    March 15th, 2008 at 8:57 am

    ,

25. links for 2008-03-29 | Moewes.com Says:
    March 29th, 2008 at 6:32 am

    , [...] Ruby, , Rails, , Web2.0 » Blog Archive » Implementing ‘15 Exercises for Learning a new Programming Language’ (tags: programming) [...]

26. Thando Vuzane - Net Age Says:
    May 8th, 2008 at 2:04 am

    , Has anyone here created a helper.rb for a vCard on Rails? Please post an example of your coding if you have.

    , Thanx!

27. Thando Vuzane - Net Age Says:
    May 9th, 2008 at 6:57 am

    , Wow, , thank you for this post. I will go home and do the ‘15 exercises for learning a new Programming Language’. And I’ll use the above coding as my reference. I’ve just recently started developing in Ruby on Rails, , so I’m at a point where I just want as many challenges and new applications to develop as possible, , because I want to fully explore RoR.

    , Thank you again, ,

28. Jeff Leitman Says:
    January 13th, 2009 at 12:17 pm

    , For a simpler UNIX solution, , you can trap SIGINT (Ctrl-C)

    i = 0
    go = true
    while go do
     print "#{i+=1}, , "
     Signal.trap("INT") do
      go = false
     end
    end
    puts "Terminated by user."
    

29. John Says:
    February 11th, 2010 at 8:33 pm

    , In response to problem 1, , interrupting an infinite sum by hitting a character:

    , Without doing threads in Ruby (like you would in Python, , for ex), , maybe you can do something simple like check for a kbhit (received character from std in) in your loop. This is a common technique when reading rs-232 serial lines on a microcontroller. You want to get data if its in a buffer, , but if it is not then you absolutely can’t hang in a get operation.

    , something like:

    , if(kbhit())
    car=getc()

    , I’m 2 hours into this language, , so I don’t know if this method exists, , but it seems like it probably does.

30. Amit Verma Says:
    October 19th, 2010 at 6:33 pm

    , Good article.

    , Also, , good reply from “Jeff Leitman” for Problem #1.

    , Thanks.

31. Purui Says:
    December 18th, 2010 at 5:47 pm

    , In #13, , first word since 2nd line will skipped. Looks like a bug.

Leave a Reply

Bad Behavior has blocked 2380 access attempts in the last 7 days.