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• Keeping updated with the latest technologies.

  - by Prashanth

  I am a software developer and I have been programming since the past six years. I simply love the mental challenge involved in trying to come up with solutions to hard problems, reading up programming literature, blogs by prominent developers and so on. I work on Microsoft platform and I have trouble keeping up with the pace at which various frameworks are rolled out. Remoting,WCF,ASP.NET,ASP.NET MVC, LINQ, WPF, WWF, OSLO, ADO.NET data services, DSL tools etc etc. Even understanding all these frameworks at an abstract level and see how they are all tied up with MS vision itself is a major hurdle. Now when you add other non microsoft technologies, programming languages etc to the equation, I wonder how do people manage? Given that there are only 24 hours in a day, how does one keep himself updated about so many technology changes that happen everyday? My question is , is it even worth doing that? The thing is, I am also interested in other fields such as literature, science. I try my best to at least gain a superficial understanding of what is happening in other fields of my interest and don't want to give up on that :)

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• EF/LINQ: Where() against a property of a subtype

  - by ladenedge

  I have a set of POCOs, all of which implement the following simple interface: interface IIdObject { int Id { get; set; } } A subset of these POCOs implement this additional interface: interface IDeletableObject : IIdObject { bool IsDeleted { get; set; } } I have a repository hierarchy that looks something like this: IRepository<T <: BasicRepository<T <: ValidatingRepository<T (where T is IIdObject) I'm trying to add a FilteringRepository to the hierarchy such that all of the POCOs that implement IDeletableObject have a Where(p => p.IsDeleted == false) filter applied before any other queries take place. My goal is to avoid duplicating the hierarchy solely for IDeletableObjects. My first attempt looked like this: public override IQueryable<T> Query() { return base.Query().Where(t => ((IDeletableObject)t).IsDeleted == false); } This works well with LINQ to Objects, but when I switch to an EF backend I get: "LINQ to Entities only supports casting Entity Data Model primitive types." I went on to try some fancier parameterized solutions, but they ultimately failed because I couldn't make T covariant in the following case for some reason I don't quite understand: interface IQueryFilter<out T> // error { Expression<Func<T, bool>> GetFilter(); } I'd be happy to go into more detail on my more complicated solutions if it would help, but I think I'll stop here for now in hope that someone might have an idea for me to try. Thanks very much in advance!

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• Why might ASP.NET be putting JavaScript in HTML Comment blocks, not CDATA?

  - by d4nt

  We have an ASP.NET 2.0 WebForms app that uses MS Ajax 1.0. It's working fine on all our environments (dev, test, IE6 VMs etc.). However, at the customer site the client side validation is not happening. We're currently trying to eliminate all the various factors and along the way we asked them to get their page source and send it to us, and we found something interesting. In our environment, our page has ASP.NET javascript in CDATA blocks: <script type="text/javascript"> //<![CDATA[ . . . //]]> </script> In their environment, the same code looks like this: <script type="text/javascript"> <!-- . . . //--> </script> This may be a red herring, but I'd like to eliminate it as the cause of the validation issues. Does anyone know whether specific configurations/patches/versions of ASP.NET will make it do this?

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• Java: Help constructing a fillTextFields() method

  - by Holly

  I have a Java project where I am to connect to a database and create buttons (next, new, save, delete, previous) to navigate through the database content where there are appropriate text fields and labels for the specific information. I'll use the code below as an example (each button is set up very similar)... I have it as follows: JButton jbtnNext = new JButton("Next ->"); jbtnNext.addActionListener(this); if (e.getSource() == jbtnNext) jbtnNext_Click(); private void jbtnNext_Click() { JOptionPane.showMessageDialog(null, "Next" ,"Button Pressed", JOptionPane.INFORMATION_MESSAGE); try { if (rset.next()) { fillTextFields(true); }else{ //Display result in a dialog box JOptionPane.showMessageDialog(null, "Not found"); } } catch (SQLException ex) { ex.printStackTrace(); } } The professor gave the following outline of logic to construct the fillTextFields() method: Construct the method to provide reusable code that would fill the JTextFields on the GUI with appropriate values from current record from the database (when "Previous or "Next" buttons are pressed) or blank values (when the new Button is pressed). To determine when the current record was to provide values (next and previous) or the value would be blank (new button) pass a boolean argument into the method. If data from the current record was to be used as fill values, pass true for both previous and next button code after moving the record pointer. If the new button was pressed and want to fill with blank values, pass false to the method. Inside the method, use a conditional expression to evaluate the boolean variable. If true, The appropriate get----() resultset method is used to fill the JTextFields. If false, fill them with "". The .setText() method of the JTextField is used to fill each JTextField. Make sure the fillTextFields method throws the appropriate exception. I understand and have the previous and next button methods passing true, while the new button method is passing false, but I don't quite understand how to set up the fillTextFields() method correctly or how to "throw the appropriate exception"... Any help would really be appreciated, thank you!

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• Project euler problem 3 in haskell

  - by shk

  I'm new in Haskell and try to solve 3 problem from http://projecteuler.net/. The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143 ? My solution: import Data.List getD :: Int -> Int getD x = -- find deviders let deriveList = filter (\y -> (x `mod` y) == 0) [1 .. x] filteredList = filter isSimpleNumber deriveList in maximum filteredList -- Check is nmber simple isSimpleNumber :: Int -> Bool isSimpleNumber x = let deriveList = map (\y -> (x `mod` y)) [1 .. x] filterLength = length ( filter (\z -> z == 0) deriveList) in case filterLength of 2 -> True _ -> False I try to run for example: getD 13195 > 29 But when i try: getD 600851475143 I get error Exception: Prelude.maximum: empty list Why? Thank you @Barry Brown, I think i must use: getD :: Integer -> Integer But i get error: Couldn't match expected type `Int' with actual type `Integer' Expected type: [Int] Actual type: [Integer] In the second argument of `filter', namely `deriveList' In the expression: filter isSimpleNumber deriveList Thank you.

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• jquery sortable with regexp

  - by Chris Lively

  I am trying to figure out the right regexp to match on list item id's. For example: <ul id="MyList" class="connectedSortable"> <li id="id=1-32">Item 1</li> <li id="id=2_23">Item 2</li> <li id="id=3">Item 3</li> <li id="id=4">Item 4</li> <li id="id=5">Item 5</li> <li id="id=6">Item 6</li> </ul> On the serialize method, I want it to pull everything after the equal sign (=) $(function () { $("#MyList, #OtherList").sortable({ connectWith: '.connectedSortable', update: function () { $("#MyListOrder").val($("#MyList").sortable('serialize', { regexp: '/(.+)[=](.+)/)' })); } }).disableSelection(); }); I tried the above, but that didn't quite work. My regexp expression is wrong and I don't know what it should be. Ideas?

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• Problems with string parameter insertion into prepared statement

  - by c0d3x

  Hi, I have a database running on an MS SQL Server. My application communicates via JDBC and ODBC with it. Now I try to use prepared statements. When I insert a numeric (Long) parameter everything works fine. When I insert a string parameter it does not work. There is no error message, but an empty result set. WHERE column LIKE ('%' + ? + '%') --inserted "test" -> empty result set WHERE column LIKE ? --inserted "%test%" -> empty result set WHERE column = ? --inserted "test" -> works But I need the LIKE functionality. When I insert the same string directly into the query string (not as a prepared statement parameter) it runs fine. WHERE column LIKE '%test%' It looks a little bit like double quoting for me, but I never used quotes inside a string. I use preparedStatement.setString(int index, String x) for insertion. What is causing this problem? How can I fix it? Thanks in advance.

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• XPath _relative_ to given element in HTMLUnit/Groovy?

  - by Misha Koshelev

  Dear All: I would like to evaluate an XPath expression relative to a given element. I have been reading here: http://www.w3schools.com/xpath/default.asp And it seems like one of the syntaxes below should work (esp no leading slash or descendant:) However, none seem to work in HTMLUnit. Any help much appreciated (oh this is a groovy script btw). Thank you! http://htmlunit.sourceforge.net/ http://groovy.codehaus.org/ Misha #!/usr/bin/env groovy import com.gargoylesoftware.htmlunit.WebClient def html=""" <html><head><title>Test</title></head> <body> <div class='levelone'> <div class='leveltwo'> <div class='levelthree' /> </div> <div class='leveltwo'> <div class='levelthree' /> <div class='levelthree' /> </div> </div> </body> </html> """ def f=new File('/tmp/test.html') if (f.exists()) { f.delete() } def fos=new FileOutputStream(f) fos<<html def webClient=new WebClient() def page=webClient.getPage('file:///tmp/test.html') def element=page.getByXPath("//div[@class='levelone']") assert element.size()==1 element=page.getByXPath("div[@class='levelone']") assert element.size()==0 element=page.getByXPath("/div[@class='levelone']") assert element.size()==0 element=page.getByXPath("descendant:div[@class='levelone']") // this gives namespace error assert element.size()==0 Thank you!!!

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• Generic validate input data via regex. Input error when match.count == 0

  - by Valamas

  Hi, I have a number of types of data fields on an input form, for example, a web page. Some fields are like, must be an email address, must be a number, must be a number between, must have certain characters. Basically, the list is undefinable. I wish to come up with a generic way of validating the data inputed. I thought I would use regex to validate the data. The fields which need validation would be related to a "regex expression" and a "regex error message" stating what the field should contain. My current mock up has that when the match count is zero, that would signify an error and to display the message. While still a white belt regex designer I have come to understand that in certain situations that it is difficult to write a regex which results in a match count of zero for every case. A complex regex case I looked for help on was Link Here. The forum post was a disaster because I confused people helping me. But one of the statements said that it was difficult to make a regex with a match count of zero meaning the input data was invalid; that the regex was very difficult to write that for. Does anyone have comments or suggestions on this generic validation system I am trying to create? thanks

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• LINQ Joins - Performance

  - by Meiscooldude

  I am curious on how exactly LINQ (not LINQ to SQL) is performing is joins behind the scenes in relation to how Sql Server performs joins. Sql Server before executing a query, generates an Execution Plan. The Execution Plan is basically an Expression Tree on what it believes is the best way to execute the query. Each node provides information on whether to do a Sort, Scan, Select, Join, ect. On a 'Join' node in our execution plan, we can see three possible algorithms; Hash Join, Merge Join, and Nested Loops Join. Sql Server will choose which algorithm to for each Join operation based on expected number of rows in Inner and Outer tables, what type of join we are doing (some algorithms don't support all types of joins), whether we need data ordered, and probably many other factors. Join Algorithms: Nested Loop Join: Best for small inputs, can be optimized with ordered inner table. Merge Join: Best for medium to large inputs sorted inputs, or an output that needs to be ordered. Hash Join: Best for medium to large inputs, can be parallelized to scale linearly. LINQ Query: DataTable firstTable, secondTable; ... var rows = from firstRow in firstTable.AsEnumerable () join secondRow in secondTable.AsEnumerable () on firstRow.Field<object> (randomObject.Property) equals secondRow.Field<object> (randomObject.Property) select new {firstRow, secondRow}; SQL Query: SELECT * FROM firstTable fT INNER JOIN secondTable sT ON fT.Property = sT.Property Sql Server might use a Nested Loop Join if it knows there are a small number of rows from each table, a merge join if it knows one of the tables has an index, and Hash join if it knows there are a lot of rows on either table and neither has an index. Does Linq choose its algorithm for joins? or does it always use one?

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• How to keep the CPU usage down while running an SDL program?

  - by budwiser

  I've done a very basic window with SDL and want to keep it running until I press the X on window. #include "SDL.h" const int SCREEN_WIDTH = 640; const int SCREEN_HEIGHT = 480; int main(int argc, char **argv) { SDL_Init( SDL_INIT_VIDEO ); SDL_Surface* screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, 0, SDL_HWSURFACE | SDL_DOUBLEBUF ); SDL_WM_SetCaption( "SDL Test", 0 ); SDL_Event event; bool quit = false; while (quit != false) { if (SDL_PollEvent(&event)) { if (event.type == SDL_QUIT) { quit = true; } } SDL_Delay(80); } SDL_Quit(); return 0; } I tried adding SDL_Delay() at the end of the while-clause and it worked quite well. However, 80 ms seemed to be the highest value I could use to keep the program running smoothly and even then the CPU usage is about 15-20%. Is this the best way to do this and do I have to just live with the fact that it eats this much CPU already on this point?

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• Usage of VIsual Memory Leak Detector

  - by Yan Cheng CHEOK

  I found a very interesting memory leak detector by using Visual C++. http://www.codeproject.com/KB/applications/visualleakdetector.aspx I try it out, but cannot make it works to detect a memory leak code. I am using MS Visual Studio 2008. Any step I had missed out? #include "stdafx.h" #include "vld.h" #include <iostream> void fun() { new int[1000]; } int _tmain(int argc, _TCHAR* argv[]) { fun(); std::cout << "lead?" << std::endl; getchar(); return 0; } The output when I run in debug mode is : ... ... 'Test.exe': Loaded 'C:\WINDOWS\WinSxS\x86_Microsoft.VC80.CRT_1fc8b3b9a1e18e3b_8.0.50727.4053_x-ww_e6967989\msvcr80.dll', Symbols loaded. 'Test.exe': Loaded 'C:\WINDOWS\system32\msvcrt.dll', Symbols loaded (source information stripped). 'Test.exe': Loaded 'C:\WINDOWS\WinSxS\x86_Microsoft.VC90.DebugCRT_1fc8b3b9a1e18e3b_9.0.30729.1_x-ww_f863c71f\msvcp90d.dll', Symbols loaded. 'Test.exe': Loaded 'C:\Program Files\Visual Leak Detector\bin\dbghelp.dll', Symbols loaded (source information stripped). Visual Leak Detector Version 1.9d installed. No memory leaks detected. Visual Leak Detector is now exiting. The program '[5468] Test.exe: Native' has exited with code 0 (0x0).

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• SQL putting two single quotes around datetime fields and fails to insert record

  - by user82613

  I am trying to INSERT into an SQL database table, but it doesn't work. So I used the SQL server profiler to see how it was building the query; what it shows is the following: declare @p1 int set @p1=0 declare @p2 int set @p2=0 declare @p3 int set @p3=1 exec InsertProcedureName @ConsumerMovingDetailID=@p1 output, @UniqueID=@p2 output, @ServiceID=@p3 output, @ProjectID=N'0', @IPAddress=N'66.229.112.168', @FirstName=N'Mike', @LastName=N'P', @Email=N'[email protected]', @PhoneNumber=N'(254)637-1256', @MobilePhone=NULL, @CurrentAddress=N'', @FromZip=N'10005', @MoveInAddress=N'', @ToZip=N'33067', @MovingSize=N'1', @MovingDate=''2009-04-30 00:00:00:000'', /* Problem here ^^^ */ @IsMovingVehicle=0, @IsPackingRequired=0, @IncludeInSaveologyPlanner=1 select @p1, @p2, @p3 As you can see, it puts a double quote two pairs of single quotes around the datetime fields, so that it produces a syntax error in SQL. I wonder if there is anything I must configure somewhere? Any help would be appreciated. Here is the environment details: Visual Studio 2008 .NET 3.5 MS SQL Server 2005 Here is the .NET code I'm using.... //call procedure for results strStoredProcedureName = "usp_SMMoverSearchResult_SELECT"; Database database = DatabaseFactory.CreateDatabase(); DbCommand dbCommand = database.GetStoredProcCommand(strStoredProcedureName); dbCommand.CommandTimeout = DataHelper.CONNECTION_TIMEOUT; database.AddInParameter(dbCommand, "@MovingDetailID", DbType.String, objPropConsumer.ConsumerMovingDetailID); database.AddInParameter(dbCommand, "@FromZip", DbType.String, objPropConsumer.FromZipCode); database.AddInParameter(dbCommand, "@ToZip", DbType.String, objPropConsumer.ToZipCode); database.AddInParameter(dbCommand, "@MovingDate", DbType.DateTime, objPropConsumer.MoveDate); database.AddInParameter(dbCommand, "@PLServiceID", DbType.Int32, objPropConsumer.ServiceID); database.AddInParameter(dbCommand, "@FromAreaCode", DbType.String, pFromAreaCode); database.AddInParameter(dbCommand, "@FromState", DbType.String, pFromState); database.AddInParameter(dbCommand, "@ToAreaCode", DbType.String, pToAreaCode); database.AddInParameter(dbCommand, "@ToState", DbType.String, pToState); DataSet dstSearchResult = new DataSet("MoverSearchResult"); database.LoadDataSet(dbCommand, dstSearchResult, new string[] { "MoverSearchResult" });

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• What is the best cross-platform language for desktop applications? (Java, Adobe Air, Flex, Silverlight??, Anything Else)

  - by Sootah

  My business partner needs a desktop application programmed, and it needs to be cross-platform as he wants Mac owners (OS X) to be able to run it as well. This, of course, is a bit of a problem for me as I program in PHP for my web projects and exclusively in C# (formerly used Visual Basic) for my desktop apps. I've been using (and love) NetBeans for my PHP stuff, and love Visual Studio just as much; they're both excellent IDEs. With this in mind, I'd like to find a language and IDE that's as similar to Visual Studio as possible (or at least something that makes development as easy as it does) for my cross-platform application development. In fact, if there is a language I can use with VS I'd be extremely happy. I realize that NetBeans has a Java Desktop App IDE, but have been having problems with it (my question in regards to that issue is here. I am also not sure that I really want to learn and use Java if there is a better, easier option out there. Obviously, the first language that came to mind that I can use cross-platform was Java, but I've also heard of people using Adobe Air, as well as Flex being used. I've never programmed in any of those languages, and as such have no frame of reference from which I can decide which would be best for me. I'm also not sure what other options there may be for me; perhaps there's another language I can use that'd be better than the three options I've already provided. (Can you make desktop apps with Silverlight? If so, did MS make an interpreter that will get them to work on OS X?) I like the syntax of C# quite a bit, and the Visual Studio IDE makes it extremely easy to make my apps with. As such, I'd like to find something that'll work as well for me with the cross-platform shatner as C# and its IDE does with my Windows apps. Thanks in advance for your help/opinions!

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• What do you mean by the expressiveness in programming lanuguage?

  - by prosseek

  I see a lot of the word 'expressiveness' when people want to stress one language is better than the other. But I don't see exactly what they mean by it. Is it the verboseness/succinctness? I mean, if one language can write down something shorter than the other, does that mean expressiveness? Please refer to my other question - http://stackoverflow.com/questions/2411772/article-about-code-density-as-a-measure-of-programming-language-power Is it the power of the language? Paul Graham says that one language is more powerful than the other language in a sense that one language can do that the other language can't do (for example, LISP can do something with macro that the other language can't do). Is it just something that makes life easier? Regular expression can be one of the examples. Is it a different way of solving the same problem: something like SQL to solve the search problem? What do you think about the expressiveness of a programming lanuage? Can you show the expressiveness using some code? What's the relationship with the expressiveness and DSL? Do people come up with DSL to get the expressiveness?

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• In which domains are message oriented middleware like AMQP useful?

  - by cocotwo

  What problem do MOM (Message Oriented Middleware) solve? Scalability? Integration? In which domain are they typically used and in which domains are they typically not used? For example, say, is Google using such solution for it's main search engine or to power GMail? What about big websites like Walmart, eBay, FedEx (pretty much a Java shop) and buy.com (pretty much an MS shop)? Does MOM solve a need there? Does it make any sense when you're writing a Webapp where you control the server-side and have an homogenous environment (say tens of Amazon EC2 instances all running Linux + Java JVMs) there and where the clients are, well, Web browsers? Does it make sense for desktop apps that need to communicate with a server? Or is it 'only' for big enterprise stuff where you typically have a happy mix of countless of different systems that needs to communicate in a way or another? I'm a bit confused as to what they're useful for and I think that with example of where they're appropriate and where they're not appropriate I could better understand their use.

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• New desktop GUI developer; can choose any platform...

  - by alexantd

  I'm planning a client-server product for a tiny, low-volume, high-cost vertical market. One of the components of the product will be a desktop application, simple to moderate in complexity, for data entry and uploading to a central server from remote PCs and/or Macs via SOAP. The server is a Java web app. Customers will be choosing their platform (Windows or Mac) based on what the client app runs on, so my options are wide-open here. However, I will be developing on a Mac and have a strong allergy to MS-specific technologies (sorry). The app will not need to run on any non-desktop-computer devices and I have total freedom to say it will support X but not Y or Z without any negative consequences (quite the luxury, to be sure). I have a lot of experience in server-side development but very little in desktop GUI stuff, and am evaluating my options on the client - basically what do I want to commit to learning over the next 6+ months. I have server-side Java experience as well as a brief dabble in iPhone development, which went OK. Overall I'm looking for: Ease of learning & development IDE support Healthy surrounding ecosystem (libraries, tools, help, etc.) Quality documentation My options as I see them, in rough order of how I'm currently mentally ranking them: Java Swing Cocoa Java SWT JavaFX Adobe AIR XULRunner Am I leaving anything out?

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• Prolog singleton variables in Python

  - by Rubens

  I'm working on a little set of scripts in python, and I came to this: line = "a b c d e f g" a, b, c, d, e, f, g = line.split() I'm quite aware of the fact that these are decisions taken during implementation, but shouldn't (or does) python offer something like: _, _, var_needed, _, _, another_var_needed, _ = line.split() as well as Prolog does offer, in order to exclude the famous singleton variables. I'm not sure, but wouldn't it avoid unnecessary allocation? Or creating references to the result of the split call does not count up as overhead? EDIT: Sorry, my point here is: in Prolog, as far as I'm concerned, in an expression like: test(L, N) :- test(L, 0, N). test([], N, N). test([_|T], M, N) :- V is M + 1, test(T, V, N). The variable represented by _ is not accessible, for what I suppose the reference to the value that does exist in the list [_|T] is not even created. But, in Python, if I use _, I can use the last value assigned to _, and also, I do suppose the assignment occurs for each of the variables _ -- which may be considered an overhead. My question here is if shouldn't there be (or if there is) a syntax to avoid such unnecessary attributions.

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• Are Java developers really paid more than .Net developers? Also, should I just try and work with C?(

  - by Jon

  Ok, so I graduated about a year and a half ago. In college days I used to be really good (and keen) on C/C++. I've even done some multithreading and socket programming in C. Created networked GUI apps for linux using GTK etc.Now,I've been working since I graduated and well, let's say, I've been stereotyped with .net. That's all I have experience with in these years (Vb.net,asp.net,javascript). I'm pretty comfortable with all of the above and also SQL server.a)Cutting to the chase, I've begun to notice how .net jobs don't seem to pay all that well as Java. Jobs seeking similar number of yrs of experience offer almost twice for java developers. Does it mean I should consider switching?b)My heart still goes out for C. As a surrogate I've tried working with VC++ 6.0 (I know they aren't the same!). I've tried my hand with DDK,SDK,COM etc. Should I try finding jobs there or am I too inexperienced. Somehow, I can't find any openings for C. Where are they? Sometimes I get frustrated and feel that maybe I should just go for MS or something. Possibly that'll help me in landing with 'fatter paying jobs' in the field that I wish to work.

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• Trying to match variables in a PHP array

  - by Nick B

  I'm stuck with a php array problem. I've to a webpage that takes values from a URL, and I need to cross reference those values against some values on the page and if they match output a 'yes'. It's an expression engine bodge job. The URL is something like domain.com/page/C12&C14 The C12 and C14 represent different categories. I've taken the last bit of the url, removed the 'C' from the values and then exploded the 12&14 into an array. I print_r the array on the page and it shows: Array ( [0] = 12 [1] = 14 ) So, the values are in the array. Lovely. Now on the page I have an html list which looks like 10 12 14 15 I want to output a YES next to the variables that are current in the array so the ideal output would be: 10 12 - YES 14 - YES 15 I was trying this but it keeps just saying No next to all of them. $currentnumber = 12; foreach ($tharray as $element) { if ($element == $currentnumber) { echo "Yes"; } else { echo "No"; } } I thought that should work, but it's not. I checked and the array and the variable are both stings. I did a strlen() on both to see if they are the same, but $currentnumber outputs '13' and the array variable outputs '2'. Any ideas as to why it's saying 13? Is the variable the wrong type of string - and if so how would I convert it?

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• Problem with circular definition in Scheme

  - by user8472

  I am currently working through SICP using Guile as my primary language for the exercises. I have found a strange behavior while implementing the exercises in chapter 3.5. I have reproduced this behavior using Guile 1.4, Guile 1.8.6 and Guile 1.8.7 on a variety of platforms and am certain it is not specific to my setup. This code works fine (and computes e): (define y (integral (delay dy) 1 0.001)) (define dy (stream-map (lambda (x) x) y)) (stream-ref y 1000) The following code should give an identical result: (define (solve f y0 dt) (define y (integral (delay dy) y0 dt)) (define dy (stream-map f y)) y) (solve (lambda (x) x) 1 0.001) But it yields the error message: standard input:7:14: While evaluating arguments to stream-map in expression (stream-map f y): standard input:7:14: Unbound variable: y ABORT: (unbound-variable) So when embedded in a procedure definition, the (define y ...) does not work, whereas outside the procedure in the global environment at the REPL it works fine. What am I doing wrong here? I can post the auxiliary code (i.e., the definitions of integral, stream-map etc.) if necessary, too. With the exception of the system-dependent code for cons-stream, they are all in the book. My own implementation of cons-stream for Guile is as follows: (define-macro (cons-stream a b) `(cons ,a (delay ,b)))

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• Avoiding mass propagation of properties and events for exposure to ViewModels.

  - by firoso

  I have an MVVM application I am developing that is to the point where I'm ready to start putting together a user interface (my client code is largely functional) I'm now running into the issue that I'm trying to get my application data to where I need it so that it can be consumed by the view model and then bound to the view. Unfortunately, it seems that I've either got a few structural oversights, or I'm just going to have to face the reality that I need to be propogating events and raising excessive amounts of errors to notify view models that thier properties have changed. Let me go into some examples of my issue: I have a class "Unit" contained in a class "Test", contained in a class "Session" contained in a class "TestManager" which is contained in "TestDataModel" which is utilized by "TestViewModel" which is databound to by my "TestView" .... WHOA. Now, consider that Unit (the bottom of the heiarchy) has a property called "Results" that is updated periodically, I want to expose that to my viewmodel and then databind it to my view, trouble is, the only way I can really think to do this is to perpetuate events WAY up a chain that say "I've been updated!" and then request the new value... This seems like an aweful way to do this. Alternatively, I could register a static event and raise it, and have the appropriate "Unit view model" grab the event and request the update. This SEEMS better... but... static events? Is that a taboo idea? Also, having an expression like: TestDataModel.TestManager.Session.Test.Unit.Results[i] Seems REALLY gross to have on a View Model. I know this all reeks of a bad design issue, but I can't figure out what I did wrong? Should I be using more singleton/container controlled lifetimes type objects? Register object instances with static helper containers? Obviously these are hard questions to answer without being intimate with the existing structure, but if you've run into situations like this, what did you do to refactor? Should I just live with this, add mass events, and propogate them?

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• JavaScript Regex: Complicated input validation

  - by ScottSEA

  I'm trying to construct a regex to screen valid part and/or serial numbers in combination, with ranges. A valid part number is a two alpha, three digit pattern or /[A-z]{2}\d{3}/ i.e. aa123 or ZZ443 etc... A valid serial number is a five digit pattern, or /\d{5}/ 13245 or 31234 and so on. That part isn't the problem. I want combinations and ranges to be valid as well: 12345, ab123,ab234-ab245, 12346 - 12349 - the ultimate goal. Ranges and/or series of part and/or serial numbers in any combination. Note that spaces are optional when specifying a range or after a comma in a series. Note that a range of part numbers has the same two letter combination on both sides of the range (i.e. ab123 - ab239) I have been wrestling with this expression for two days now, and haven't come up with anything better than this: /^(?:[A-z]{2}\d{3}[, ]*)|(?:\d{5}[, ]*)|(?:([A-z]{2})\d{3} ?- ?\4\d{3}[, ]*)|(?:\d{5} ?- ?\d{5}[, ]*)$/ ... My Regex-Fu is weak.

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• Not able to scroll the listbox in WP7.

  - by Shaireen

  I have a listbox control where items are added using a user control having a textblock and image. <UserControl xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d" FontFamily="{StaticResource PhoneFontFamilyNormal}" FontSize="{StaticResource PhoneFontSizeNormal}" Foreground="{StaticResource PhoneForegroundBrush}" d:DesignHeight="52" d:DesignWidth="480"> <Grid x:Name="LayoutRoot" Background="{StaticResource PhoneChromeBrush}"> <TextBlock Height="30" HorizontalAlignment="Left" Margin="12,10,0,0" Name="Index_itemtext" Text="" VerticalAlignment="Top" Width="145" /> <Image Height="34" HorizontalAlignment="Right" Margin="0,6,55,0" Source="blue_triangle.png" Name="IndexList_itemImage" Stretch="Uniform" VerticalAlignment="Top" Width="66" /> <Line Height="10" HorizontalAlignment="Left" Margin="0,38,0,0" Name="seperator_line" Stroke="White" StrokeThickness="2" VerticalAlignment="Top" Width="480" Stretch="Fill" Fill="#FFF5E9E9" /> </Grid> And the list box xaml: <ListBox Name="Index_list" ScrollViewer.VerticalScrollBarVisibility="Visible" VerticalContentAlignment="Top" SelectionChanged="on_selection" Margin="0,78,0,0"> </ListBox> Now when i add the items to the list ,the vertical scroll does not go till the last item i.e. it comes back to first row which stops from last item selection: for (int i = 0; i < gridSize; i++) { listbox_item list_item = new listbox_item(); list_item.Index_itemtext.FontSize = 25; list_item.Index_itemtext.Text = index[i]; list_item.IndexList_itemImage.Source = new BitmapImage(new Uri("some.png", UriKind.Relative)); list_item.seperator_line.StrokeThickness = 5; list_item.Margin = new Thickness(0, 0, 0, 5); Index_list.Items.Add(list_item); } Also the list row does not occupy the width of device in landscape mode,whereas the requirement is that the row item widens as the device width changes.Can someone help with these problems?

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• java.math.BigInteger pow(exponent) question

  - by Jan Kraus

  Hi, I did some tests on pow(exponent) method. Unfortunately, my math skills are not strong enough to handle the following problem. I'm using this code: BigInteger.valueOf(2).pow(var); Results: var | time in ms 2000000 | 11450 2500000 | 12471 3000000 | 22379 3500000 | 32147 4000000 | 46270 4500000 | 31459 5000000 | 49922 See? 2,500,000 exponent is calculated almost as fast as 2,000,000. 4,500,000 is calculated much faster then 4,000,000. Why is that? To give you some help, here's the original implementation of BigInteger.pow(exponent): public BigInteger pow(int exponent) { if (exponent < 0) throw new ArithmeticException("Negative exponent"); if (signum==0) return (exponent==0 ? ONE : this); // Perform exponentiation using repeated squaring trick int newSign = (signum<0 && (exponent&1)==1 ? -1 : 1); int[] baseToPow2 = this.mag; int[] result = {1}; while (exponent != 0) { if ((exponent & 1)==1) { result = multiplyToLen(result, result.length, baseToPow2, baseToPow2.length, null); result = trustedStripLeadingZeroInts(result); } if ((exponent >>>= 1) != 0) { baseToPow2 = squareToLen(baseToPow2, baseToPow2.length, null); baseToPow2 = trustedStripLeadingZeroInts(baseToPow2); } } return new BigInteger(result, newSign); }

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