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• urgent..haskell mini interpreter

  - by mohamed elshikh

  i'm asked to implement this project and i have problems in part b which is the eval function this is the full describtion of the project You are required to implement an interpreter for mini-Haskell language. An interpreter is dened in Wikipedia as a computer program that executes, i.e. performs, instructions written in a programming language. The interpreter should be able to evaluate functions written in a special notation, which you will dene. A function is dened by: Function name Input Parameters : dened as a list of variables. The body of the function. The body of the function can be any of the following statements: a) Variable: The function may return any of the input variables. b) Arithmetic Expressions: The arithmetic expressions include input variables and addition, sub- traction, multiplication, division and modulus operations on arithmetic expressions. c) Boolean Expressions: The Boolean expressions include the ordering of arithmetic expressions (applying the relationships: <, =<, , = or =) and the anding, oring and negation of Boolean expressions. d) If-then-else statements: where the if keyword is followed by a Boolean expression. The then and else parts may be followed by any of the statements described here. e) Guarded expressions: where each case consists of a boolean expression and any of the statements described here. The expression consists of any number of cases. The rst case whose condition is true, its body should be evaluated. The guarded expression has to terminate with an otherwise case. f) Function calls: the body of the function may have a call to another function. Note that all inputs passed to the function will be of type Int. The output of the function can be of type Int or Bool. To implement the interpreter, you are required to implement the following: a) Dene a datatype for the following expressions: Variables Arithmetic expressions Boolean expressions If-then-else statements Guarded expressions Functions b) Implement the function eval which evaluates a function. It takes 3 inputs: The name of a function to be evaluated represented as a string. A list of inputs to that function. The arguments will always be of datatype Int. A list of functions. Each function is represented as instance of the datatype that you have created for functions. c) Implement the function get_type that returns the type of the function (as a string). The input to this function is the same as in part b. here is what i've done data Variable = v(char) data Arth= va Variable | Add Arth Arth | Sub Arth Arth | Times Arth Arth | Divide Arth Arth data Bol= Great Arth Arth | Small Arth Arth | Geq Arth Arth | Seq Arth Arth | And Bol Bol | Or Bol Bol | Neg Bol data Cond = data Guard = data Fun =cons String [Variable] Body data Body= bodycons(String) |Bol |Cond |Guard |Arth

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• Algorithm: Determine shape of two sectors delineated by an arbitrary path, and then fill one.

  - by Arseniy Banayev

  NOTE: This is a challenging problem for anybody who likes logic problems, etc. Consider a rectangular two-dimensional grid of height H and width W. Every space on the grid has a value, either 0 1 or 2. Initially, every space on the grid is a 0, except for the spaces along each of the four edges, which are initially a 2. Then consider an arbitrary path of adjacent (horizontally or vertically) grid spaces. The path begins on a 2 and ends on a different 2. Every space along the path is a 1. The path divides the grid into two "sectors" of 0 spaces. There is an object that rests on an unspecified 0 space. The "sector" that does NOT contain the object must be filled completely with 2. Define an algorithm that determines the spaces that must become 2 from 0, given an array (list) of values (0, 1, or 2) that correspond to the values in the grid, going from top to bottom and then from left to right. In other words, the element at index 0 in the array contains the value of the top-left space in the grid (initially a 2). The element at index 1 contains the value of the space in the grid that is in the left column, second from the top, and so forth. The element at index H contains the value of the space in the grid that is in the top row but second from the left, and so forth. Once the algorithm finishes and the empty "sector" is filled completely with 2s, the SAME algorithm must be sufficient to do the same process again. The second (and on) time, the path is still drawn from a 2 to a different 2, across spaces of 0, but the "grid" is smaller because the 2s that are surrounded by other 2s cannot be touched by the path (since the path is along spaces of 0). I thank whomever is able to figure this out for me, very very much. This does not have to be in a particular programming language; in fact, pseudo-code or just English is sufficient. Thanks again! If you have any questions, just leave a comment and I'll specify what needs to be specified.

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• Is it Bad Practice to use C++ only for the STL containers?

  - by gmatt

  First a little background ... In what follows, I use C,C++ and Java for coding (general) algorithms, not gui's and fancy program's with interfaces, but simple command line algorithms and libraries. I started out learning about programming in Java. I got pretty good with Java and I learned to use the Java containers a lot as they tend to reduce complexity of book keeping while guaranteeing great performance. I intermittently used C++, but I was definitely not as good with it as with Java and it felt cumbersome. I did not know C++ enough to work in it without having to look up every single function and so I quickly reverted back to sticking to Java as much as possible. I then made a sudden transition into cracking and hacking in assembly language, because I felt I was concentrated too much attention on a much too high level language and I needed more experience with how a CPU interacts with memory and whats really going on with the 1's and 0's. I have to admit this was one of the most educational and fun experiences I've had with computers to date. For obviously reasons, I could not use assembly language to code on a daily basis, it was mostly reserved for fun diversions. After learning more about the computer through this experience I then realized that C++ is so much closer to the "level of 1's and 0's" than Java was, but I still felt it to be incredibly obtuse, like a swiss army knife with far too many gizmos to do any one task with elegance. I decided to give plain vanilla C a try, and I quickly fell in love. It was a happy medium between simplicity and enough "micromanagent" to not abstract what is really going on. However, I did miss one thing about Java: the containers. In particular, a simple container (like the stl vector) that expands dynamically in size is incredibly useful, but quite a pain to have to implement in C every time. Hence my code currently looks like almost entirely C with containers from C++ thrown in, the only feature I use from C++. I'd like to know if its consider okay in practice to use just one feature of C++, and ignore the rest in favor of C type code?

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• How to Integrate C++ compiler in Visual Studio 2008

  - by Kasun

  Hi Can someone help me with this issue? I currently working on my project for final year of my honors degree. And we are developing a application to evaluate programming assignments of student ( for 1st year student level) I just want to know how to integrate C++ compiler using C# code to compile C++ code. In our case we are loading a student C++ code into text area, then with a click on button we want to compile the code. And if there any compilation errors it will be displayed on text area nearby. (Interface is attached herewith.) And finally it able to execute the code if there aren't any compilation errors. And results will be displayed in console. We were able to do this with a C#(C# code will be loaded to text area intead of C++ code) code using inbuilt compiler. But still not able to do for C# code. Can anyone suggest a method to do this? It is possible to integrate external compiler to VS C# code? If possible how to achieve it? Very grateful if anyone will contributing to solve this matter? This is code for Build button which we proceed with C# code compiling CodeDomProvider codeProvider = CodeDomProvider.CreateProvider("csharp"); string Output = "Out.exe"; Button ButtonObject = (Button)sender; rtbresult.Text = ""; System.CodeDom.Compiler.CompilerParameters parameters = new CompilerParameters(); //Make sure we generate an EXE, not a DLL parameters.GenerateExecutable = true; parameters.OutputAssembly = Output; CompilerResults results = codeProvider.CompileAssemblyFromSource(parameters, rtbcode.Text); if (results.Errors.Count > 0) { rtbresult.ForeColor = Color.Red; foreach (CompilerError CompErr in results.Errors) { rtbresult.Text = rtbresult.Text + "Line number " + CompErr.Line + ", Error Number: " + CompErr.ErrorNumber + ", '" + CompErr.ErrorText + ";" + Environment.NewLine + Environment.NewLine; } } else { //Successful Compile rtbresult.ForeColor = Color.Blue; rtbresult.Text = "Success!"; //If we clicked run then launch our EXE if (ButtonObject.Text == "Run") Process.Start(Output); // Run button }

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• C++ include statement required if defining a map in a headerfile.

  - by Justin

  I was doing a project for computer course on programming concepts. This project was to be completed in C++ using Object Oriented designs we learned throughout the course. Anyhow, I have two files symboltable.h and symboltable.cpp. I want to use a map as the data structure so I define it in the private section of the header file. I #include <map> in the cpp file before I #include "symboltable.h". I get several errors from the compiler (MS VS 2008 Pro) when I go to debug/run the program the first of which is: Error 1 error C2146: syntax error : missing ';' before identifier 'table' c:\users\jsmith\documents\visual studio 2008\projects\project2\project2\symboltable.h 22 Project2 To fix this I had to #include <map> in the header file, which to me seems strange. Here are the relevant code files: // symboltable.h #include <map> class SymbolTable { public: SymbolTable() {} void insert(string variable, double value); double lookUp(string variable); void init(); // Added as part of the spec given in the conference area. private: map<string, double> table; // Our container for variables and their values. }; and // symboltable.cpp #include <map> #include <string> #include <iostream> using namespace std; #include "symboltable.h" void SymbolTable::insert(string variable, double value) { table[variable] = value; // Creates a new map entry, if variable name already exist it overwrites last value. } double SymbolTable::lookUp(string variable) { if(table.find(variable) == table.end()) // Search for the variable, find() returns a position, if thats the end then we didnt find it. throw exception("Error: Uninitialized variable"); else return table[variable]; } void SymbolTable::init() { table.clear(); // Clears the map, removes all elements. }

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• jquery load a specific #Div content from multiple html files

  - by Vikram

  Hello friends I am trying to make a Content Slider for my site. I have multiple HTML files and the structure of these files is like this: <div id="title"><h2>Title of the Slide</h2></div> <div id="image"><a href="http://mylink.com"><img src="image.jpg" width="600" height="300" alt="image"</a></div> <div id="content">Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s.</div> I have been trying to use the following script get content (but no success): <?php function render($position="") { ob_start(); foreach(glob("/slides/*.html") as $fileName) { $fname = basename( $fileName ); $curArr = file($fname); $slides[$fname ]['title'] = $curArr[0]; $slides[$fname ]['image'] = $curArr[1]; $slides[$fname ]['content'] = $curArr[2]; foreach($slides as $key => $value){ ?> <div id="slide-title"> <?php echo $value['title'] ?> </div> <div id="slide-content"> <?php echo $value['image'] ?> </div> <div id="slide-image"> <?php echo $value['content'] ?> </div> <?php }} ?> <?php return ob_get_clean(); } But then I came to know about a jQuery function.... (again no success) jQuery.noConflict(); (function($){ $(document).ready(function () { $('#slide-title').load('slides/slide1.html #title'); $('#slide-content').load('slides/slide1.html #content'); $('#slide-image').load('slides/slide1.html #image'); }); })(jQuery); Now My questions are..... Am I using the right syntax. How do I get the content from multiple files using jQuery. Please Note : My knowledge on Programming is almost '0'. I have just started learning it.

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• Downloading large file with php

  - by Alessandro

  Hi, I have to write a php script to download potentially large files. The file I'm reporting here works fine most of the times. However, if the client's connection is slow the request ends (with status code 200) in the middle of the downloading, but not always at the very same point, and not at the very same time. I tried to overwrite some php.ini variables (see the first statements) but the problem remains. I don't know if it's relevant but my hosting server is SiteGround, and for simple static file requests, the download works fine also with slow connections. I've found Forced downloading large file with php but I didn't understand mario's answer. I'm new to web programming. So here's my code. <?php ini_set('memory_limit','16M'); ini_set('post_max_size', '30M'); set_time_limit(0); include ('../private/database_connection.php'); $downloadFolder = '../download/'; $fileName = $_POST['file']; $filePath = $downloadFolder . $fileName; if($fileName == NULL) { exit; } ob_start(); session_start(); if(!isset($_SESSION['Username'])) { // or redirect to login (remembering this download request) $_SESSION['previousPage'] = 'download.php?file=' . $fileName; header("Location: login.php"); exit; } if (file_exists($filePath)) { header('Content-Description: File Transfer'); header('Content-Type: application/octet-stream'); //header('Content-Disposition: attachment; filename='.$fileName); header("Content-Disposition: attachment; filename=\"$fileName\""); header('Content-Transfer-Encoding: binary'); header('Expires: 0'); header('Cache-Control: must-revalidate, post-check=0, pre-check=0'); //header('Pragma: public'); header('Content-Length: ' . filesize($filePath)); ob_clean(); flush(); // download // 1 // readfile($filePath); // 2 $file = @fopen($filePath,"rb"); if ($file) { while(!feof($file)) { print(fread($file, 1024*8)); flush(); if (connection_status()!=0) { @fclose($file); die(); } } @fclose($file); } exit; } else { header('HTTP/1.1 404 File not found'); exit; } ?>

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• Can I make a LaTeX macro 'return' a filename?

  - by drfrogsplat

  I'm writing my thesis/dissertation and since its an on-going work I don't always have the actual images ready for the figures I put into my document, but for various reasons want to automatically have it substitute a dummy figure in place when the included graphics file doesn't exist. E.g. I can do something like \includegraphics[width=8cm]{\chapdir/figures/fluxcapacitor} (where \chapdir is a macro for my 'current' chapter directory, e.g. \def\chapdir{./ch_timetravel} and if there's no ./ch_timetravel/figures/fluxcapacitor.jpg it'll insert ./commands/dummy.jpg instead. I've structured my macros (perhaps naïvely?) so that I have a macro (\figFileOrDummy) that determines the appropriate file to include by checking if the argument provided to it exists, so that I can call \includegraphics[properties]{\figFileOrDummy{\chapdir/figures/fluxcapacitor}}. Except I'm getting various errors depending on how I try to call this, which seem to suggest that I'm approaching the problem in a fundamentally flawed way as far as 'good LaTeX programming' goes. Here's the macro to check if the file exists (and 'return' either filename or the dummy filename): \newcommand{\figFileOrDummy}[1]{% % Figure base name (no extension) to be used if the file exists \def\fodname{#1}% \def\dummyfig{commands/dummy}% % Check if output is PS (.EPS) or PDF (.JPG/.PDF/.PNG/...) figures \ifx\pdfoutput\undefined% % EPS figures only \IfFileExists{\fodname.eps}{}{\def\fodname{\dummyfig}}% \else% % Check existence of various extensions: PDF, TIF, TIFF, JPG, JPEG, PNG, MPS \def\figtest{0}% flag below compared to this value \IfFileExists{\fodname.pdf}{\def\figfilenamefound{1}}{\def\figfilenamefound{0}}% \IfFileExists{\fodname.jpg}{\def\figfilenamefound{1}}{}% \IfFileExists{\fodname.png}{\def\figfilenamefound{1}}{}% % and so on... % If no files found matching the filename (flag is 0) then use the dummy figure \ifx\figfilenamefound\figtest% \def\fodname{\dummyfig}% \fi% \fi% % 'return' the filename \fodname% }% Alternatively, here's a much simpler version which seems to have similar problems: \newcommand{\figFileOrDummy}[1]{% \def\dummyfig{commands/dummy}% \dummyfig% } The \def commands seems to be processed after the expansion of the macro they're trying to define, so it ends up being \def {commands/dummy}... (note the space after \def) and obviously complains. Also it seems to treat the literal contents of the macro as the filename for \includegraphics, rather than resolving/expanding it first, so complains that the file '\def {commands/dummy}... .png' doesn't exist.. I've tried also doing something like \edef\figfilename{\figFileOrDummy{\chapdir/figures/fluxcapacitor}} to try to force it to make \figfilename hold just the value rather than the full macro, but I get an Undefined control sequence error complaining the variables I'm trying to \def in the \figFileOrDummy macro are undefined. So my question is either How do I make this macro expand properly?; or If this is the wrong way of structuring my macros, how should I actually structure such a macro, in order to be able to insert dummy/real figures automatically?; or Is there a package that already handles this type of thing nicely that I've overlooked? I feel like I'm missing something pretty fundamental here...

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• What are the pros and cons of using manual list iteration vs recursion through fail

  - by magus

  I come up against this all the time, and I'm never sure which way to attack it. Below are two methods for processing some season facts. What I'm trying to work out is whether to use method 1 or 2, and what are the pros and cons of each, especially large amounts of facts. methodone seems wasteful since the facts are available, why bother building a list of them (especially a large list). This must have memory implications too if the list is large enough ? And it doesn't take advantage of Prolog's natural backtracking feature. methodtwo takes advantage of backtracking to do the recursion for me, and I would guess would be much more memory efficient, but is it good programming practice generally to do this? It's arguably uglier to follow, and might there be any other side effects? One problem I can see is that each time fail is called, we lose the ability to pass anything back to the calling predicate, eg. if it was methodtwo(SeasonResults), since we continually fail the predicate on purpose. So methodtwo would need to assert facts to store state. Presumably(?) method 2 would be faster as it has no (large) list processing to do? I could imagine that if I had a list, then methodone would be the way to go.. or is that always true? Might it make sense in any conditions to assert the list to facts using methodone then process them using method two? Complete madness? But then again, I read that asserting facts is a very 'expensive' business, so list handling might be the way to go, even for large lists? Any thoughts? Or is it sometimes better to use one and not the other, depending on (what) situation? eg. for memory optimisation, use method 2, including asserting facts and, for speed use method 1? season(spring). season(summer). season(autumn). season(winter). % Season handling showseason(Season) :- atom_length(Season, LenSeason), write('Season Length is '), write(LenSeason), nl. % ------------------------------------------------------------- % Method 1 - Findall facts/iterate through the list and process each %-------------------------------------------------------------- % Iterate manually through a season list lenseason([]). lenseason([Season|MoreSeasons]) :- showseason(Season), lenseason(MoreSeasons). % Findall to build a list then iterate until all done methodone :- findall(Season, season(Season), AllSeasons), lenseason(AllSeasons), write('Done'). % ------------------------------------------------------------- % Method 2 - Use fail to force recursion %-------------------------------------------------------------- methodtwo :- % Get one season and show it season(Season), showseason(Season), % Force prolog to backtrack to find another season fail. % No more seasons, we have finished methodtwo :- write('Done').

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• How to design service that can provide interface as JAX-WS web service, or via JMS, or as local meth

  - by kevinegham

  Using a typical JEE framework, how do I develop and deploy a service that can be called as a web service (with a WSDL interface), be invoked via JMS messages, or called directly from another service in the same container? Here's some more context: Currently I am responsible for a service (let's call it Service X) with the following properties: Interface definition is a human readable document kept up-to-date manually. Accepts HTTP form-encoded requests to a single URL. Sends plain old XML responses (no schema). Uses Apache to accept requests + a proprietary application server (not servlet or EJB based) containing all logic which runs in a seperate tier. Makes heavy use of a relational database. Called both by internal applications written in a variety of languages and also by a small number of third-parties. I want to (or at least, have been told to!): Switch to a well-known (pref. open source) JEE stack such as JBoss, Glassfish, etc. Split Service X into Service A and Service B so that we can take Service B down for maintenance without affecting Service A. Note that Service B will depend on (i.e. need to make requests to) Service A. Make both services easier for third parties to integrate with by providing at least a WS-I style interface (WSDL + SOAP + XML + HTTP) and probably a JMS interface too. In future we might consider a more lightweight API too (REST + JSON? Google Protocol Buffers?) but that's a nice to have. Additional consideration are: On a smaller deployment, Service A and Service B will likely to running on the same machine and it would seem rather silly for them to use HTTP or a message bus to communicate; better if they could run in the same container and make method calls to each other. Backwards compatibility with the existing ad-hoc Service X interface is not required, and we're not planning on re-using too much of the existing code for the new services. I'm happy with either contract-first (WSDL I guess) or (annotated) code-first development. Apologies if my terminology is a bit hazy - I'm pretty experienced with Java and web programming in general, but am finding it quite hard to get up to speed with all this enterprise / SOA stuff - it seems I have a lot to learn! I'm also not very used to using a framework rather than simply writing code that calls some packages to do things. I've got as far as downloading Glassfish, knocking up a simple WSDL file and using wsimport + a little dummy code to turn that into a WAR file which I've deployed.

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• Syntax error while copying an multidimensional array to another in C

  - by mantuko

  We are programming a ST269 microcontroller which has two IR distance sensors. To calibrate these sensors we made one table for each sensor with the distance we measured and the corresponding value we get from the ADC. Now we want to use one function to approximate the values in between. So we defined two two-dimensional arrays (one for each sensor) as global variables. In our function we then want to copy the one array we want to work with to a working array and approximate our values. So here's the code: ... unsigned int ir_werte_re[][] = { {8,553}, ... {83,133} }; unsigned int ir_werte_li[][] = { {8,566}, ... {83,147} }; ... unsigned int geradenaproximation(unsigned int messwert, unsigned int seite) { unsigned int working_array[16][16]; unsigned int i = 0; if (seite == 0) { for (i = 0; i < sizeof(working_array); i++) { working_array[i][0] = ir_werte_li[i][0]; i++; } } else { for (i = 0; i < sizeof(working_array); i++) { working_array[i][0] = ir_werte_re[i][0]; i++; } } i = 0; unsigned int y1 = 0; unsigned int x1 = 0; ... } This code is in a file called sensor.c. We didn't write anything about our global arrays in the sensor.h should we? The sensor.h of course is included in our main.c and there the function is called. We also tried to copy the arrays via memcpy(working_array, ir_werte_li, sizeof(working_array)); And in every way we do this we get a syntax error near unsigned in the line where we're declaring unsigned int y1 = 0; and I'm pretty sure that there is no syntax error in this line : ) The last time I spend coding in C is a few years away so I'm not sure if the way we try to do this is good. Perhaps we can solve this by using a pointer instead of really copying the array or something. So please help me out I'll appreciate your bits on this.

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• A two player game over the intranet..

  - by Santwana

  Hi everybody.. I am a student of 3rd year engineering and only a novice in my programming skills. I need some help with my project.. I wish to develop a two player game to be played over the network (Intranet). I want to develop a simple website with a few html pages for this.My ideas for the project run as follows: 1.People can log in from different systems and check who ever is online on the network currently. the page also shows who is playing with whom. 2.If a person is interested in playing with a player who is currently online, he sends a request of which the other player is somehow notified( using a message or an alert on his profile page..) 3.If the player accepts the request, a game is started. This is exactly where I am clueless.. How can I make them play the game? I need to develop a turn based game with two players, eg chessboard.. how can I do this? The game has to be played live.. and it is time tracked. i need your help with coding the above.. the other features i wish to include are: 4.The game could not be abruptly terminated by any one if the users.The request to terminate the game should be sent to the other player first and only if he accepts can the game be terminated. Whoever wins the game would get a plus 10 on their credit and if he terminated he gets a minus 10. The credits remains constant even if he loses but the success percentage is reduced. 6.The player with highest winning percentage is projected as the player of the week on the home page and he can post a challenge to all others.. I only have an intermediate knowledge of core java and know the basics of Swing and Awt. I am not at all familiar with networking in java right now. I have 5 to 6 weeks of time for developing the project but I hope to learn the things before I start my project. i would prefer to use a lan to illustrate the project and I know only java,jsp,oracle,html and bit of xml to develop my proj. Also I wish to know if I can code this within 6 weeks, would it be too difficult or complicated? Please spare some time to tell me. Please.. please.. I need your suggestions and help.. thank you so much..

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• Authlogic Help! Registering a new user when currently logged-in as a user not working.

  - by looloobs

  Hi Just as a disclaimer I am new to rails and programming in general so apologize for misunderstanding something obvious. I have Authlogic with activation up and running. So for my site I would like my users who are logged in to be able to register other users. The new user would pick their login and password through the activation email, but the existing user needs to put them in by email, position and a couple other attributes. I want that to be done by the existing user. The problem I am running into, if I am logged in and then try and create a new user it just tries to update the existing user and doesn't create a new one. I am not sure if there is some way to fix this by having another session start??? If that is even right/possible I wouldn't know how to go about implementing it. I realize without knowing fully about my application it may be difficult to answer this, but does this even sound like the right way to go about this? Am I missing something here? Users Controller: class UsersController < ApplicationController before_filter :require_no_user, :only => [:new, :create] before_filter :require_user, :only => [:show, :edit, :update] def new @user = User.new end def create @user = User.new if @user.signup!(params) @user.deliver_activation_instructions! flash[:notice] = "Your account has been created. Please check your e-mail for your account activation instructions!" redirect_to profile_url else render :action => :new end end def show @user = @current_user end def edit @user = @current_user end def update @user = @current_user # makes our views "cleaner" and more consistent if @user.update_attributes(params[:user]) flash[:notice] = "Account updated!" redirect_to profile_url else render :action => :edit end end end My User_Session Controller: class UserSessionsController < ApplicationController before_filter :require_no_user, :only => [:new, :create] before_filter :require_user, :only => :destroy def new @user_session = UserSession.new end def create @user_session = UserSession.new(params[:user_session]) if @user_session.save flash[:notice] = "Login successful!" if @user_session.user.position == 'Battalion Commander' : redirect_to battalion_path(@user_session.user.battalion_id) else end else render :action => :new end end def destroy current_user_session.destroy flash[:notice] = "Logout successful!" redirect_back_or_default new_user_session_url end end

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• Implementing hoverIntent for Drop Down Menu (coming from click_event)

  - by stormeTrooper

  I've just recently started programming, I was hoping for some help. I have a drop down menu that was originally activated by click_event, however I want to now implement hoverIntent in order to make the menu drop. The issue I am having now is being able to use the menu, because whenever I invoke the menu now, once I leave the area that activates the menu, the menu closes. If you could explain to me like I'm five, I'd appreciate it, thanks :) The code I am using as follows: JavaScript: function setupUserConfigMenu() { $('.user_profile_btn').hoverIntent( function (event) { $('#user_settings_dropdown').animate({height:['toggle', 'swing'] }, 225); }, function (event) { $('#user_settings_dropdown').animate({height:['toggle', 'swing'] }, 225); }) } HTML: <li> <a href="<%= "#" %>" class="user_profile_btn" title="Your profile page"><%= truncate(current_user.full_name || current_user.name, :length => 28) %> <div class="arrow_down"></div></a> <ul id="user_settings_dropdown"> <li> <a href="<%= current_user.get_url(true) %>"> <%= image_tag current_user.get_thumb_url, :size => "30x30" %> <div> <%= truncate(current_user.full_name || current_user.name, :length => 40) %> <br> View profile </div> </a> </li> <div class="grey_line"></div> <li class="settings_list_item"> <%= link_to "Settings", edit_user_registration_path %> </li> <li class="settings_list_item"> <%= link_to "About", "/about" %> </li> <li class="settings_list_item"> <%= link_to "Logout", destroy_user_session_path, :method => :delete %> </li> </ul> </li>

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• circles and triangles problem

  - by Faken

  Hello everyone, I have an interesting problem here I've been trying to solve for the last little while: I have 3 circles on a 2D xy plane, each with the same known radius. I know the coordinates of each of the three centers (they are arbitrary and can be anywhere). What is the largest triangle that can be drawn such that each vertice of the triangle sits on a separate circle, what are the coordinates of those verticies? I've been looking at this problem for hours and asked a bunch of people but so far only one person has been able to suggest a plausible solution (though i have no way of proving it). The solution that we have come up with involves first creating a triangle about the three circle centers. Next we look at each circle individually and calculate the equation of a line that passes through the circle's center and is perpendicular to the opposite edge. We then calculate two intersection points of the circle. This is then done for the next two circles with a result of 6 points. We iterate over the 8 possible 3 point triangles that these 6 points create (the restriction is that each point of the big triangle must be on a separate circle) and find the maximum size. The results look reasonable (at least when drawn out on paper) and it passes the special case of when the centers of the circles all fall on a straight line (gives a known largest triangle). Unfortunate i have no way of proving this is correct or not. I'm wondering if anyone has encountered a problem similar to this and if so, how did you solve it? Note: I understand that this is mostly a math question and not programming, however it is going to be implemented in code and it must be optimized to run very fast and efficient. In fact, I already have the above solution in code and tested to be working, if you would like to take a look, please let me know, i chose not to post it because its all in vector form and pretty much impossible to figure out exactly what is going on (because it's been condensed to be more efficient). Lastly, yes this is for school work, though it is NOT a homework question/assignment/project. It's part of my graduate thesis (abet a very very small part, but still technically is part of it). Thanks for your help.

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• How Should I Generate Trade Statistics For CouchDB/Rails3 Application?

  - by James

  My Problem: I am trying to developing a web application for currency traders. The application allows traders to enter or upload information about their trades and I want to calculate a wide variety of statistics based on what the user entered. Now, normally I would use a relational database for this, but I have two requirements that don't fit well with a relational database so I am attempting to use couchdb. Those two problems are: 1) Primarily, I have a companion desktop application that users will be able to work with and replicate to the site using couchdb's awesome replication feature and 2) I would like to allow users to be able to define their own custom things to track about trades and generate results based off of what they enter. The schema less nature of couch seems perfect here, but it may end up being harder than it sounds. (I already know couch requires you to define views in advance and such so I was just planning on sticking all the custom attributes in an array and then emitting the array in the view and further processing from there.) What I Am Doing: Right now I am just emitting each trade in couch keyed by each user's system and querying with the key of the system to get an array of trades per system. Simple. I am not using a reduce function currently to calculate any stats because I couldn't figure out how to get everything I need without getting a reduce overflow error. Here is an example of rows that are getting emitted from couch: {"total_rows":134,"offset":0,"rows":[ {"id":"5b1dcd47221e160d8721feee4ccc64be", "key":["80e40ba2fa43589d57ec3f1d19db41e6","2010/05/14 04:32:37 +0000"], null, "doc":{ "_id":"5b1dcd47221e160d8721feee4ccc64be", "_rev":"1-bc9fe763e2637694df47d6f5efb58e5b", "couchrest-type":"Trade", "system":"80e40ba2fa43589d57ec3f1d19db41e6", "pair":"EUR/USD", "direction":"Buy", "entry":12600, "exit":12700, "stop_loss":12500, "profit_target":12700, "status":"Closed", "slug":"101332132375", "custom_tracking": [{"name":"signal", "value":"Pin Bar"}] "updated_at":"2010/05/14 04:32:37 +0000", "created_at":"2010/05/14 04:32:37 +0000", "result":100}} ]} In my rails 3 controller I am basically just populating an array of trades such as the one above and then extracting out the relevant data into smaller arrays that I can compute my statistics on. Here is my show action for the page that I want to display the stats and all the trades: def show @trades = Trade.by_system(:startkey => [@system.id], :endkey => [@system.id, Time.now ]) @trades.each do |trade| if trade.result > 0 @winning_trades << trade.result elsif trade.result < 0 @losing_trades << trade.result else @breakeven_trades << trade.result end if trade.direction == "Buy" @long_trades << trade.result else @short_trades << trade.result end if trade["custom_tracking"] != nil @custom_tracking << {"result" => trade.result, "variables" => trade["custom_tracking"]} end end end I am omitting some other stuff that is going on, but that is the gist of what I am doing. Then I am calculating stuff in the view layer to produce some results: <% winning_long_trades = @long_trades.reject {|trade| trade <= 0 } %> <% winning_short_trades = @short_trades.reject {|trade| trade <= 0 } %> <ul> <li>Total Trades: <%= @trades.count %></li> <li>Winners: <%= @winning_trades.size %></li> <li>Biggest Winner (Pips): <%= @winning_trades.max %></li> <li>Average Win(Pips): <%= @winning_trades.sum/@winning_trades.size %></li> <li>Losers: <%= @losing_trades.size %></li> <li>Biggest Loser (Pips): <%= @losing_trades.min %></li> <li>Average Loss(Pips): <%= @losing_trades.sum/@losing_trades.size %></li> <li>Breakeven Trades: <%= @breakeven_trades.size %></li> <li>Long Trades: <%= @long_trades.size %></li> <li>Winning Long Trades: <%= winning_long_trades.size %></li> <li>Short Trades: <%= @short_trades.size %></li> <li>Winning Short Trades: <%= winning_short_trades.size %></li> <li>Total Pips: <%= @winning_trades.sum + @losing_trades.sum %></li> <li>Win Rate (%): <%= @winning_trades.size/@trades.count.to_f * 100 %></li> </ul> This produces the following results, which aside from a few things is exactly what I want: Total Trades: 134 Winners: 70 Biggest Winner (Pips): 1488 Average Win(Pips): 440 Losers: 58 Biggest Loser (Pips): -516 Average Loss(Pips): -225 Breakeven Trades: 6 Long Trades: 125 Winning Long Trades: 67 Short Trades: 9 Winning Short Trades: 3 Total Pips: 17819 Win Rate (%): 52.23880597014925 What I Am Wondering- Finally The Actual Questions: I am starting to get really skeptical of how well this method will work when a user has 5,000 trades instead of just 134 like in this example. I anticipate most users will only have somewhere under 200 per year, but some users may have a couple thousand trades per year. Probably no more than 5,000 per year. It seems to work ok now, but the page load times are already getting a tad high for my tastes. (About 800ms to generate the page according to rails logs with about a 250ms of that spent in the view layer.) I will end up caching this page I am sure, but I still need the regenerate the page each time a trade is updated and I can't afford to have this be too slow. Sooo..... Is doing something similar here possible with a straight couchdb reduce function? I am assuming handing this off to couch would possibly help with larger data sets. I couldn't figure out how, but I suppose that doesn't mean it isn't possible. If possible, any hints will be helpful. Could I use a list function if a reduce was not available due to reduce constraints? Are couchdb list functions suitable for this type of calculations? Anyone have any idea of whether or not list functions perform well? Any hints what one would look like for the type of calculations I am trying to achieve? I thought about other options such as running the calculations at the time each trade was saved or nightly if I had to and saving the results to a statistics doc that I could then query so that all the processing was done ahead of time. I would like this to be the last resort because then I can't really filter out trades by time periods dynamically like I would really like to. (I want to have a slider that a user can slide to only show trades from that time period using the startkey and endkey in couchdb if I can.) If I should continue running the calculations inside the rails app at the time of the page view, what can I do to improve my current implementation. I am new to rails, couch and programming in general. I am sure that I could be doing something better here. Do I need to create an array for each stat or is there a better way to do that. I guess I just would really like some advice on how to tackle this problem. I want to keep the page generation time minimal since I anticipate these being some of the highest trafficked pages. My gut is that I will need to offload the statistics calculation to either couch or run the stats in advance of when they are called, but I am not sure. Lastly: Like I mentioned above, one of the primary reasons for using couch is to allow users to define their own things to track per trade. Getting the data into couch is no problem, but how would I be able to take the custom_tracking array and find how many winning trades for each named tracking attribute. If anyone can give me any hints to the possibility of doing this that would be great. Thanks a bunch. Would really appreciate any help. Willing to fork out some $$$ if someone wants to take on the problem for me. (Don't know if that is allowed on stack overflow or not.)

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• Pure sine wave inverter

  - by Nick

  Not exactly programming (sorry) but I think it's pretty close and can be of interest to other programmers. I'm trying to setup a battery power station so that I can work from anywhere. I go surfing a lot and my idea is to be able to work from wherever I can park my car (given there's coverage). So, I'm getting a deep cycle battery, a 240V charger (I'm in Australia), and an inverter. At the back of my laptop it says 19V and 4.62A. From the people I've spoken to that means it consumes about 90W at most. So my inverter needs to be able to output about 100W. Most of them seem to be 200W and up so this shouldn't be a problem. I want to be able run my laptop for 10 hours (plus the 2 hours I get from the laptop battery) straight. According to the people I've spoken to and from what I gather online I need a battery that has the amp hours for my "amp draw". I have no idea how to calculate this but I've been guesstimating. Most deep cycle batteries seem to be classified using amp hours (Ah)... 35Ah, 50Ah, 75Ah, 100Ah, and so on. However the amp hours on those batteries is for a 240V and I seem to be using 19V. According to an expert I spoke to you'd need a 100Ah battery to power a 5A appliance at 240V for 10 hours (you only get about 50% useful power). That to me is 5A * 240V = 100Ah battery. So, naive as I might be I take 240V and divide that by my 19V and reach the conclusion that I can get away with a battery that's about 12 times smaller than that 100Ah. The expert told me I needed a 50Ah battery so that's probably what I'll be getting, but it would be interesting to know what I theoretically would need to power my laptop for 10 hours. As for charging the battery the expert I spoke to said I needed a 3-5A charger to be able to charge that 50Ah battery from flat to full in about 10 hours (I will just leave it plugged in over night). Now to my question. The expert said it's not a matter of "if" more like a guaranteed "when" my computer will stuff up if I don't use a "pure sine wave inverter". From what I gather the power that comes out of that battery is not as clean as the power we get in the socket at home. Apparently it's "square" and the one in the socket is nice and smooth. I've already got an inverter, but it's not "pure". Do I really need to buy the $200-300 pure sine wave inverter or can I get away with something else? Perhaps the laptop adapter that sits in the middle of my laptop power cable already fixes that wave to be nice and smooth? Thanks!

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• issues regarding UAC prompt

  - by peter

  I want to implement a UAC prompt for an application in visualc++ the operating system is 32bit x7460(2processor) Windowsserver 2008 the exe is myproject.exe through manifest.. Here for testing i wl build the application in Windows XP OS and copy the exe in to system containg the Windowsserver 2008 machine and replace it So what i did is i added a manifest like this name of that is myproject.exe.manifest My project has 3 folders like Headerfile,Resourcefile and Source file.I added this manifest(myproject.exe.manifest) in the Sourcefile folder containing other cpp and c code <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0"> <assemblyIdentity version="4.0" processorArchitecture="X7460" name="myproject" type="win32"/> <description>myproject Problem</description> <!-- Identify the application security requirements. --> <trustInfo xmlns="urn:schemas-microsoft-com:asm.v2"> <security> <requestedPrivileges> <requestedExecutionLevel level="requireAdministrator" uiAccess="false"/> </requestedPrivileges> </security> </trustInfo> </assembly> then i added this line of code in Resourcefile(.rc).Means one header file is there(Myproject.h).I added the line of code there #define MANIFEST_RESOURCE_ID 1 MANIFEST_RESOURCE_ID RT_MANIFEST "myproject.exe.manifest" Finally i did the following step Under Project, select Properties. 3. In Properties, select Manifest Tool, and then select Input and Output. 4. Add in the name of your application manifest file under Additional manifest files. 5. Rebuild your application. But i am getting lot of Syntax errors Is there any problems in the way which i followed.If i commented the line #define MANIFEST_RESOURCE_ID 1 MANIFEST_RESOURCE_ID RT_MANIFEST "myproject.exe.manifest" which added in Myproject.h for adding values in .rc file there willnot any error other than this general error c1010070: Failed to load and parse the manifest. The system cannot find the file specified. .\myproject.exe.manifest How to enable UAC prompt through programming

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• Linux termios VTIME not working?

  - by San Jacinto

  We've been bashing our heads off of this one all morning. We've got some serial lines setup between an embedded linux device and an Ubuntu box. Our reads are getting screwed up because our code usually returns two (sometimes more, sometimes exactly one) message reads instead of one message read per actual message sent. Here is the code that opens the serial port. InterCharTime is set to 4. void COMBaseClass::OpenPort() { cerr<< "openning port"<< port <<"\n"; struct termios newtio; this->fd = -1; int fdTemp; fdTemp = open( port, O_RDWR | O_NOCTTY); if (fdTemp < 0) { portOpen = 0; cerr<<"problem openning "<< port <<". Retrying"<<endl; usleep(1000000); return; } newtio.c_cflag = BaudRate | CS8 | CLOCAL | CREAD ;//| StopBits; newtio.c_iflag = IGNPAR; newtio.c_oflag = 0; /* set input mode (non-canonical, no echo,...) */ newtio.c_lflag = 0; newtio.c_cc[VTIME] = InterCharTime; /* inter-character timer in .1 secs */ newtio.c_cc[VMIN] = readBufferSize; /* blocking read until 1 char received */ tcflush(fdTemp, TCIFLUSH); tcsetattr(fdTemp,TCSANOW,&newtio); this->fd = fdTemp; portOpen = 1; } The other end is configured similarly for communication, and has one small section of particular iterest: while (1) { sprintf(out, "\r\nHello world %lu", ++ulCount); puts(out); WritePort((BYTE *)out, strlen(out)+1); sleep(2); } //while Now, when I run a read thread on the receiving machine, "hello world" is usually broken up over a couple messages. Here is some sample output: 1: Hello 2: world 1 3: Hello 4: world 2 5: Hello 6: world 3 where number followed by a colon is one message recieved. Can you see any error we are making? Thank you. Edit: For clarity, please view section 3.2 of this resource href="http://www.faqs.org/docs/Linux-HOWTO/Serial-Programming-HOWTO.html. To my understanding, with a VTIME of a couple seconds (meaning vtime is set anywhere between 10 and 50, trial-and-error), and a VMIN of 1, there should be no reason that the message is broken up over two separate messages.

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• Multiple choice test GUI with serialization of Q&A

  - by Bobby

  I'm working on a project for school in Java programming. I need to design a GUI that will take in questions and answers and store them in a file. It should be able to contain an unlimited number of questions. We have covered binary I/O. How do I write the input they give to a file? How would I go about having them add multiple questions from this GUI? package multiplechoice; import java.awt.*; import javax.swing.*; public class MultipleChoice extends JFrame { public MultipleChoice() { /* * Setting Layout */ setLayout(new GridLayout(10,10)); /* * First Question */ add(new JLabel("What is the category of the question?: ")); JTextField category = new JTextField(); add(category); add(new JLabel("Please enter the question you wish to ask: ")); JTextField question = new JTextField(); add(question); add(new JLabel("Please enter the correct answer: ")); JTextField correctAnswer = new JTextField(); add(correctAnswer); add(new JLabel("Please enter a reccomended answer to display: ")); JTextField reccomendedAnswer = new JTextField(); add(reccomendedAnswer); add(new JLabel("Please enter a choice for multiple choice option " + "A")); JTextField A = new JTextField(); add(A); add(new JLabel("Please enter a choice for multiple choice option " + "B")); JTextField B = new JTextField(); add(B); add(new JLabel("Please enter a choice for multiple choice option " + "C")); JTextField C = new JTextField(); add(C); add(new JLabel("Please enter a choice for multiple choice option " + "D")); JTextField D = new JTextField(); add(D); add(new JButton("Compile Questions")); add(new JButton("Next Question")); } public static void main(String[] args) { /* * Creating JFrame to contain questions */ FinalProject frame = new FinalProject(); // FileOutputStream output = new FileOutputStream("Questions.dat"); JPanel panel = new JPanel(); // button.setLayout(); // frame.add(panel); panel.setSize(100,100); // button.setPreferredSize(new Dimension(100,100)); frame.setTitle("FinalProject"); frame.setSize(600, 400); frame.setLocationRelativeTo(null); // Center the frame frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); } }

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• Making an efficient algorithm

  - by James P.

  Here's my recent submission for the FB programming contest (qualifying round only requires to upload program output so source code doesn't matter). The objective is to find two squares that add up to a given value. I've left it as it is as an example. It does the job but is too slow for my liking. Here's the points that are obviously eating up time: List of squares is being recalculated for each call of getNumOfDoubleSquares(). This could be precalculated or extended when needed. Both squares are being checked for when it is only necessary to check for one (complements). There might be a more efficient way than a double-nested loop to find pairs. Other suggestions? Besides this particular problem, what do you look for when optimizing an algorithm? public static int getNumOfDoubleSquares( Integer target ){ int num = 0; ArrayList<Integer> squares = new ArrayList<Integer>(); ArrayList<Integer> found = new ArrayList<Integer>(); int squareValue = 0; for( int j=0; squareValue<=target; j++ ){ squares.add(j, squareValue); squareValue = (int)Math.pow(j+1,2); } int squareSum = 0; System.out.println( "Target=" + target ); for( int i = 0; i < squares.size(); i++ ){ int square1 = squares.get(i); for( int j = 0; j < squares.size(); j++ ){ int square2 = squares.get(j); squareSum = square1 + square2; if( squareSum == target && !found.contains( square1 ) && !found.contains( square2 ) ){ found.add(square1); found.add(square2); System.out.println( "Found !" + square1 +"+"+ square2 +"="+ squareSum); num++; } } } return num; }

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• How should I ethically approach user password storage for later plaintext retrieval?

  - by Shane

  As I continue to build more and more websites and web applications I am often asked to store user's passwords in a way that they can be retrieved if/when the user has an issue (either to email a forgotten password link, walk them through over the phone, etc.) When I can I fight bitterly against this practice and I do a lot of ‘extra’ programming to make password resets and administrative assistance possible without storing their actual password. When I can’t fight it (or can’t win) then I always encode the password in some way so that it at least isn’t stored as plaintext in the database—though I am aware that if my DB gets hacked that it won’t take much for the culprit to crack the passwords as well—so that makes me uncomfortable. In a perfect world folks would update passwords frequently and not duplicate them across many different sites—unfortunately I know MANY people that have the same work/home/email/bank password, and have even freely given it to me when they need assistance. I don’t want to be the one responsible for their financial demise if my DB security procedures fail for some reason. Morally and ethically I feel responsible for protecting what can be, for some users, their livelihood even if they are treating it with much less respect. I am certain that there are many avenues to approach and arguments to be made for salting hashes and different encoding options, but is there a single ‘best practice’ when you have to store them? In almost all cases I am using PHP and MySQL if that makes any difference in the way I should handle the specifics. Additional Information for Bounty I want to clarify that I know this is not something you want to have to do and that in most cases refusal to do so is best. I am, however, not looking for a lecture on the merits of taking this approach I am looking for the best steps to take if you do take this approach. In a note below I made the point that websites geared largely toward the elderly, mentally challenged, or very young can become confusing for people when they are asked to perform a secure password recovery routine. Though we may find it simple and mundane in those cases some users need the extra assistance of either having a service tech help them into the system or having it emailed/displayed directly to them. In such systems the attrition rate from these demographics could hobble the application if users were not given this level of access assistance, so please answer with such a setup in mind. Thanks to Everyone This has been a fun questions with lots of debate and I have enjoyed it. In the end I selected an answer that both retains password security (I will not have to keep plain text or recoverable passwords), but also makes it possible for the user base I specified to log into a system without the major drawbacks I have found from normal password recovery. As always there were about 5 answers that I would like to have marked correct for different reasons, but I had to choose the best one--all the rest got a +1. Thanks everyone!

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• Realtime MySQL search results on an advanced search page

  - by Andrew Heath

  I'm a hobbyist, and started learning PHP last September solely to build a hobby website that I had always wished and dreamed another more competent person might make. I enjoy programming, but I have little free time and enjoy a wide range of other interests and activities. I feel learning PHP alone can probably allow me to create 98% of the desired features for my site, but that last 2% is awfully appealing: The most powerful tool of the site is an advanced search page that picks through a 1000+ record game scenario database. Users can data-mine to tremendous depths - this advanced page has upwards of 50 different potential variables. It's designed to allow the hardcore user to search on almost any possible combination of data in our database and it works well. Those who aren't interested in wading through the sea of options may use the Basic Search, which is comprised of the most popular parts of the Advanced search. Because the advanced search is so comprehensive, and because the database is rather small (less than 1,200 potential hits maximum), with each variable you choose to include the likelihood of getting any qualifying results at all drops dramatically. In my fantasy land where I can wield AJAX as if it were Excalibur, my users would have a realtime Total Results counter in the corner of their screen as they used this page, which would automatically update its query structure and report how many results will be displayed with the addition of each variable. In this way it would be effortless to know just how many variables are enough, and when you've gone and added one that zeroes out the results set. A somewhat similar implementation, at least visually, would be the Subtotal sidebar when building a new custom computer on IBuyPower.com For those of you actually still reading this, my question is really rather simple: Given the time & ability constraints outlined above, would I be able to learn just enough AJAX (or whatever) needed to pull this one feature off without too much trouble? would I be able to more or less drop-in a pre-written code snippet and tweak to fit? or should I consider opening my code up to a trusted & capable individual in the future for this implementation? (assuming I can find one...) Thank you.

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• .Net Custom Components "disappear" after file save

  - by EatATaco

  I might have a hard time explaining this because I am at a total loss for what is happening so I am just looking for some guidance. I might be a bit wordy because I don't know exactly what is the relevant information. I am developing a GUI for a project that I am working on in using .Net (C#) Part of the interface mimics, exactly, what we do in another product. For consistency reasons, my boss wants me to make it look the same way. So I got the other software and basically copied and pasted the components into my new GUI. This required me to introduce a component library (the now defunct Graphics Server GSNet, so I can't go to them for help) so I could implement some simple graphs and temperature/pressure "widgets." The components show up fine, and when I compile, everything seems to work fine. However, at some point during my programming it just breaks. Sometimes the tab that these components are on starts throwing exceptions when I view the designer page (A missing method exception) so it won't display. Sometimes JUST those components from the GSNet library don't show up. Sometimes, if I try to run it, I get a not-instantiated exception on one of their lines of code in the designer code file. Sometimes I can't view the designer at all. No matter what I do I can't reverse it. Even if I undo what I just did it won't fix it. If it happens, I have to revert to a backup and start over again. So I started to backup pretty much every step. I compile it and it works. I comment out a line of code, save it, and then uncomment that same line of code (so I am working with the same exact code) and the components all disappear. It doesn't matter what line of code I actually comment out, as long as it is in the same project that these components are being used. I pretty much have to use the components. . . so does anyone have any suggestion or where I can look to debug this?

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• Java Flow Control Problem

  - by Kyle_Solo

  I am programming a simple 2d game engine. I've decided how I'd like the engine to function: it will be composed of objects containing "events" that my main game loop will trigger when appropriate. A little more about the structure: Every GameObject has an updateEvent method. objectList is a list of all the objects that will receive update events. Only objects on this list have their updateEvent method called by the game loop. I’m trying to implement this method in the GameObject class (This specification is what I’d like the method to achieve): /** * This method removes a GameObject from objectList. The GameObject * should immediately stop executing code, that is, absolutely no more * code inside update events will be executed for the removed game object. * If necessary, control should transfer to the game loop. * @param go The GameObject to be removed */ public void remove(GameObject go) So if an object tries to remove itself inside of an update event, control should transfer back to the game engine: public void updateEvent() { //object's update event remove(this); System.out.println("Should never reach here!"); } Here’s what I have so far. It works, but the more I read about using exceptions for flow control the less I like it, so I want to see if there are alternatives. Remove Method public void remove(GameObject go) { //add to removedList //flag as removed //throw an exception if removing self from inside an updateEvent } Game Loop for(GameObject go : objectList) { try { if (!go.removed) { go.updateEvent(); } else { //object is scheduled to be removed, do nothing } } catch(ObjectRemovedException e) { //control has been transferred back to the game loop //no need to do anything here } } // now remove the objects that are in removedList from objectList 2 questions: Am I correct in assuming that the only way to implement the stop-right-away part of the remove method as described above is by throwing a custom exception and catching it in the game loop? (I know, using exceptions for flow control is like goto, which is bad. I just can’t think of another way to do what I want!) For the removal from the list itself, it is possible for one object to remove one that is farther down on the list. Currently I’m checking a removed flag before executing any code, and at the end of each pass removing the objects to avoid concurrent modification. Is there a better, preferably instant/non-polling way to do this?

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