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• Big Oh Notation - formal definition.

  - by aloh

  I'm reading a textbook right now for my Java III class. We're reading about Big-Oh and I'm a little confused by its formal definition. Formal Definition: "A function f(n) is of order at most g(n) - that is, f(n) = O(g(n)) - if a positive real number c and positive integer N exist such that f(n) <= c g(n) for all n = N. That is, c g(n) is an upper bound on f(n) when n is sufficiently large." Ok, that makes sense. But hold on, keep reading...the book gave me this example: "In segment 9.14, we said that an algorithm that uses 5n + 3 operations is O(n). We now can show that 5n + 3 = O(n) by using the formal definition of Big Oh. When n = 3, 5n + 3 <= 5n + n = 6n. Thus, if we let f(n) = 5n + 3, g(n) = n, c = 6, N = 3, we have shown that f(n) <= 6 g(n) for n = 3, or 5n + 3 = O(n). That is, if an algorithm requires time directly proportional to 5n + 3, it is O(n)." Ok, this kind of makes sense to me. They're saying that if n = 3 or greater, 5n + 3 takes less time than if n was less than 3 - thus 5n + n = 6n - right? Makes sense, since if n was 2, 5n + 3 = 13 while 6n = 12 but when n is 3 or greater 5n + 3 will always be less than or equal to 6n. Here's where I get confused. They give me another example: Example 2: "Let's show that 4n^2 + 50n - 10 = O(n^2). It is easy to see that: 4n^2 + 50n - 10 <= 4n^2 + 50n for any n. Since 50n <= 50n^2 for n = 50, 4n^2 + 50n - 10 <= 4n^2 + 50n^2 = 54n^2 for n = 50. Thus, with c = 54 and N = 50, we have shown that 4n^2 + 50n - 10 = O(n^2)." This statement doesn't make sense: 50n <= 50n^2 for n = 50. Isn't any n going to make the 50n less than 50n^2? Not just greater than or equal to 50? Why did they even mention that 50n <= 50n^2? What does that have to do with the problem? Also, 4n^2 + 50n - 10 <= 4n^2 + 50n^2 = 54n^2 for n = 50 is going to be true no matter what n is. And how in the world does picking numbers show that f(n) = O(g(n))? Please help me understand! :(

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• Database Schema Versioning Strategies

  - by Jack Ryan

  I work on a project that uses a reasonably large database, the live version weighing in at somewhere around 60-80GB. The live database is the only real definitive source of our schema, and because of its size duplicating this database is too slow to be done often. This means we have ended up developing our database schema in a pretty ad hoc way, using sql compare to migrate changes from dev dbs to the live system, and only wiping our dev dbs every month or two. I am hoping to get some pointers on how to improve our database development work flow so that we have a little more control. Some things to think about: Currently nobody is really in charge of the database schema, all developers can change it if they need to, though generally these decisions are talked about before they are done. There are stored procedures, functions, and views in the database. These should probably be dumped to files so they can be reloaded on every build. Schema changes should probably be checked in as scripts. We have started to do this recently. However all our scripts must then be numbered (because there may be dependencies between them), and must be re runnable (because our build script currently runs them all in order). This makes them hard to read because they are full of conditionals that check whether tables or columns already exist. This is a step that is often forgotten by developers. Getting a new database should be quick and easy. This is currently a big problem, it takes several hours to get a copy of last nights backup and restore it onto a dev machine. Some mechanism needs to be in place to allow developers to update static data. We have tables that contain data that is never updated through the application, but does potentially need to be changed when we do a new release (often this drives dropdowns). The whole thing needs to be runnable as part of a build script. Are there any tools that can be used to help to do this? Eventually I would like to be at a point where a new DB can be built from scratch without copying any data from the live system. I don't mind writing some scripts to glue all the steps together but each part should be easily editable so that we continue to use it rather than make changes directly on DBs.

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• Finding good heuristic for A* search

  - by Martin

  I'm trying to find the optimal solution for a little puzzle game called Twiddle (an applet with the game can be found here). The game has a 3x3 matrix with the number from 1 to 9. The goal is to bring the numbers in the correct order using the minimum amount of moves. In each move you can rotate a 2x2 square either clockwise or counterclockwise. I.e. if you have this state 6 3 9 8 7 5 1 2 4 and you rotate the upper left 2x2 square clockwise you get 8 6 9 7 3 5 1 2 4 I'm using a A* search to find the optimal solution. My f() is simply the number of rotations need. My heuristic function already leads to the optimal solution but I don't think it's the best one you can find. My current heuristic takes each corner, looks at the number at the corner and calculates the manhatten distance to the position this number will have in the solved state (which gives me the number of rotation needed to bring the number to this postion) and sums all these values. I.e. You take the above example: 6 3 9 8 7 5 1 2 4 and this end state 1 2 3 4 5 6 7 8 9 then the heuristic does the following 6 is currently at index 0 and should by at index 5: 3 rotations needed 9 is currently at index 2 and should by at index 8: 2 rotations needed 1 is currently at index 6 and should by at index 0: 2 rotations needed 4 is currently at index 8 and should by at index 3: 3 rotations needed h = 3 + 2 + 2 + 3 = 10 But there is the problem, that you rotate 4 elements at once. So there a rare cases where you can do two (ore more) of theses estimated rotations in one move. This means theses heuristic overestimates the distance to the solution. My current workaround is, to simply excluded one of the corners from the calculation which solves this problem at least for my test-cases. I've done no research if really solves the problem or if this heuristic still overestimates in same edge-cases. So my question is: What is the best heuristic you can come up with? (Disclaimer: This is for a university project, so this is a bit of homework. But I'm free to use any resource if can come up with, so it's okay to ask you guys. Also I will credit Stackoverflow for helping me ;) )

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• Passing variables, creating instances, self, The mechanics and usage of classes: need explenation

  - by Baf

  I've been sitting over this the whole day and Im a little tired already so please excuse me being brief. Im new to python. I just rewrrote a working program, into a bunch of functions in a class and everzthings messed up. I dont know if its me but Im very surprised i couldn t find a beginners tutorial on how to handle classes on the web so I have a few questions. First of all, in the init section of the class i have declared a bunch of variables with self.variable=something. Is it correct that i should be able to access/modify these variables in every function of the class by using self.variable in that function? In other words by declaring self.variable i have made these variables, global variables in the scope of the class right? If not how do i handle self. ? Secondly how do i correctly pass arguments to the class? some example code would be cool. thirdly how do i call a function of the class outside of the class scope? some example code would be cool. fouthly how do I create an Instance of the class INITIALCLASS in another class OTHERCLASS, passing variables from OTHERCLASS to INITIALCLASS? some example code would be cool. I Want to call a function from OTHERCLASS with arguments from INITIALCLASS. What Ive done so far is. class OTHERCLASS(): def __init__(self,variable1,variable2,variable3): self.variable1=variable1 self.variable2=variable2 self.variable3=variable3 def someotherfunction(self): something=somecode(using self.variable3) self.variable2.append(something) print self.variable2 def somemorefunctions(self): self.variable2.append(variable1) class INITIALCLASS(): def __init__(self): self.variable1=value1 self.variable2=[] self.variable3='' self.DoIt=OTHERCLASS(variable1,variable2,variable3) def somefunction(self): variable3=Somecode #tried this self.DoIt.someotherfunctions() #and this DoIt.someotherfunctions() I clearly havent understood how to pass variables to classes or how to handle self, when to use it and when not, I probably also havent understood how to properly create an isntance of a class. In general i havent udnerstood the mechanics of classes So please help me and explain it to me like i have no Idea( which i dont it seems). Or point me to a thorough video, or readable tutorial. All i find on the web is super simple examples, that didnt help me much. Or just very short definitions of classes and class methods instances etc. I can send you my original code if you guys want, but its quite long. Thanks for the Help Much appreciated!

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• Device drivers and Windows

  - by b-gen-jack-o-neill

  Hi, I am trying to complete the picture of how the PC and the OS interacts together. And I am at point, where I am little out of guess when it comes to device drivers. Please, don´t write things like its too complicated, or you don´t need to know when using high programming laguage and winapi functions. I want to know, it´s for study purposes. So, the very basic structure of how OS and PC (by PC I mean of course HW) is how I see it is that all other than direct CPU commands, which can CPU do on itself (arithmetic operation, its registers access and memory access) must pass thru OS. Mainly becouse from ring level 3 you cannot use in and out intructions which are used for acesing other HW. I know that there is MMIO,but it must be set by port comunication first. It was not like this all the time. Even I am bit young to remember MSDOS, I know you could access HW directly, becouse there ws no limitation, no ring mode. So you could to write string to diplay use wheather DOS function, or directly acess video card memory and write it by yourself. But as OS developed, there is no longer this possibility. But it is fine, since OS now handles all the HW comunication, and frankly it more convinient and much more safe (I would say the only option) in multitasking environment. So nowdays you instead of using int instructions to use BIOS mapped function or DOS function you call dll which internally than handles everything you don´t need to know about. I understand this. I also undrstand that device drivers is the piece of code that runs in ring level 0, so it can do all the HW interactions. But what I don´t understand is connection between OS and device driver. Let´s take a example - I want to make a sound card make a sound. So I call windows API to acess sound card, but what happens than? Does windows call device drivers to do so? But if it does call device driver, does it mean, that all device drivers which can be called by winAPI function, must have routines named in some specific way? I mean, when I have new sound card, must its drivers have functions named same as the old one? So Windows can actually call the same function from its perspective? But if Windows have predefined sets of functions requored by device drivers, that it cannot use new drivers that doesent existed before last version of OS came out. Please, help me understand this mess. I am really getting mad. Thanks.

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• Cannot .Count() on IQueryable (NHibernate)

  - by Bruno Reis

  Hello, I'm with an irritating problem. It might be something stupid, but I couldn't find out. I'm using Linq to NHibernate, and I would like to count how many items are there in a repository. Here is a very simplified definition of my repository, with the code that matters: public class Repository { private ISession session; /* ... */ public virtual IQueryable<Product> GetAll() { return session.Linq<Product>(); } } All the relevant code in the end of the question. Then, to count the items on my repository, I do something like: var total = productRepository.GetAll().Count(); The problem is that total is 0. Always. However there are items in the repository. Furthermore, I can .Get(id) any of them. My NHibernate log shows that the following query was executed: SELECT count(*) as y0_ FROM [Product] this_ WHERE not (1=1) That must be that "WHERE not (1=1)" clause the cause of this problem. What can I do to be able .Count() the items in my repository? Thanks! EDIT: Actually the repository.GetAll() code is a little bit different... and that might change something! It is actually a generic repository for Entities. Some of the entities implement also the ILogicalDeletable interface (it contains a single bool property "IsDeleted"). Just before the "return" inside the GetAll() method I check if if the Entity I'm querying implements ILogicalDeletable. public interface IRepository<TEntity, TId> where TEntity : Entity<TEntity, TId> { IQueryable<TEntity> GetAll(); ... } public abstract class Repository<TEntity, TId> : IRepository<TEntity, TId> where TEntity : Entity<TEntity, TId> { public virtual IQueryable<TEntity> GetAll() { if (typeof (ILogicalDeletable).IsAssignableFrom(typeof (TEntity))) { return session.Linq<TEntity>() .Where(x => (x as ILogicalDeletable).IsDeleted == false); } else { return session.Linq<TEntity>(); } } } public interface ILogicalDeletable { bool IsDeleted {get; set;} } public Product : Entity<Product, int>, ILogicalDeletable { ... } public IProductRepository : IRepository<Product, int> {} public ProductRepository : Repository<Product, int>, IProductRepository {} Edit 2: actually the .GetAll() is always returning an empty result-set for entities that implement the ILogicalDeletable interface (ie, it ALWAYS add a WHERE NOT (1=1) clause. I think Linq to NHibernate does not like the typecast.

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• Object relationships

  - by Hammerstein

  This stems from a recent couple of posts I've made on events and memory management in general. I'm making a new question as I don't think the software I'm using has anything to do with the overall problem and I'm trying to understand a little more about how to properly manage things. This is ASP.NET. I've been trying to understand the needs for Dispose/Finalize over the past few days and believe that I've got to a stage where I'm pretty happy with when I should/shouldn't implement the Dispose/Finalize. 'If I have members that implement IDisposable, put explicit calls to their dispose in my dispose method' seems to be my understanding. So, now I'm thinking maybe my understanding of object lifetimes and what holds on to what is just wrong! Rather than come up with some sample code that I think will illustrate my point, I'm going to describe as best I can actual code and see if someone can talk me through it. So, I have a repository class, in it I have a DataContext that I create when the repository is created. I implement IDisposable, and when my calling object is done, I call Dispose on my repository and explicitly call DataContext.Dispose( ). Now, one of the methods of this class creates and returns a list of objects that's handed back to my front end. Front End - Controller - Repository - Controller - Front End. (Using Redgate Memory Profiler, I take a snapshot of my software when the page is first loaded). My front end creates a controller object on page load and then makes a request to the repository sending back a list of items. When the page is finished loading, I call Dispose on the controller which in turn calls dispose on the context. In my mind, that should mean that my connection is closed and that I have no instances of my controller class. If I then refresh the page, it jumps to two 'Live' instances of the controller class. If I look at the object retention graph, the objects I created in my call to the list are being held onto ultimately by what looks like Linq. The controller/repository aside, if I create a list of objects somewhere, or I create an object and return it somewhere, am I safe to just assume that .NET will eventually come and clean things up for me or is there a best practice? The 'Live' instances suggest to me that these are still in memory and active objects, the fact that RMP apparently forces GC doesn't mean anything?

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• organizing unit test

  - by soulmerge

  I have found several conventions to housekeeping unit tests in a project and I'm not sure which approach would be suitable for our next PHP project. I am trying to find the best convention to encourage easy development and accessibility of the tests when reviewing the source code. I would be very interested in your experience/opinion regarding each: One folder for productive code, another for unit tests: This separates unit tests from the logic files of the project. This separation of concerns is as much a nuisance as it is an advantage: Someone looking into the source code of the project will - so I suppose - either browse the implementation or the unit tests (or more commonly: the implementation only). The advantage of unit tests being another viewpoint to your classes is lost - those two viewpoints are just too far apart IMO. Annotated test methods: Any modern unit testing framework I know allows developers to create dedicated test methods, annotating them (@test) and embedding them in the project code. The big drawback I see here is that the project files get cluttered. Even if these methods are separated using a comment header (like UNIT TESTS below this line) it just bloats the class unnecessarily. Test files within the same folders as the implementation files: Our file naming convention dictates that PHP files containing classes (one class per file) should end with .class.php. I could imagine that putting unit tests regarding a class file into another one ending on .test.php would render the tests much more present to other developers without tainting the class. Although it bloats the project folders, instead of the implementation files, this is my favorite so far, but I have my doubts: I would think others have come up with this already, and discarded this option for some reason (i.e. I have not seen a java project with the files Foo.java and FooTest.java within the same folder.) Maybe it's because java developers make heavier use of IDEs that allow them easier access to the tests, whereas in PHP no big editors have emerged (like eclipse for java) - many devs I know use vim/emacs or similar editors with little support for PHP development per se. What is your experience with any of these unit test placements? Do you have another convention I haven't listed here? Or am I just overrating unit test accessibility to reviewing developers?

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• Keeping Velocity Constant and Player in Position - Sidescrolling

  - by user2904951

  I'm working on a Little Mobile Game with Cocos2D-X and Box2D. The Point where I got stuck is the movement of a box2d-body (the main actor) and the according Sprite. Now I want to : move this Body with a constant velocity along the x-axis, no matter if it's rolling (it's a circleshape) upwards or downwards keep the body nearly sticking to the ground on which it's rolling keep the Body and the according Sprite in the Center of the Screen. What I tried : in the update()- method I used body->SetLinearVelocity(b2Vec2(x,y)) to higher/lower values, if the Body was passing a constant value for his velocity I used to set very high y-Values in body->SetLinearVelocity(b2Vec2(x,y)) First tried to use CCFollow with my playerSprite, which was also Scrolling along the y-axis, as i only need to scroll along the x-axis, so I decided to move the whole layer which is containing the ambience (platforms etc.) to the left of my Screen and my Player Body & Player sprite to the right of the Screen, adjusting the speed values to Keep the Player in the Center of the Screen. Well... ...didn't work as i wanted it to, because each time i set the velocity manually (I also tried to use body->applyLinearImpulse(...) when the Body is moving upwards just as playing around with the value of velocityIterations in world->Step(...)) there's a small delay, which pushes the player Body more or less further of the Center of the Screen. ... didn't also work as I expected it to, because I needed to adjust the x-Values, when the Body was moving upwards to Keep it not getting slowed down, this made my Body even less sticky to the ground.... ... CCFollow did a good Job, except that I didn't want to scroll along the y-axis also and it Forces the overgiven sprite to start in the Center of the Screen. Moving the whole Layer even brought no good results, I have tried a Long time to adjust values of the movement Speed of the layer and the Body to Keep it negating each other, that the player stays nearly in the Center of the Screen.... So my question is : Does anyone of you have any Kind of new Approach for me to solve this cohesive bunch of Problems ? Cheers, Seb

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• How to use unset() for this Linear Linked List in PHP

  - by Peter

  I'm writing a simple linear linked list implementation in PHP. This is basically just for practice... part of a Project Euler problem. I'm not sure if I should be using unset() to help in garbage collection in order to avoid memory leaks. Should I include an unset() for head and temp in the destructor of LLL? I understand that I'll use unset() to delete nodes when I want, but is unset() necessary for general clean up at any point? Is the memory map freed once the script terminates even if you don't use unset()? I saw this SO question, but I'm still a little unclear. Is the answer that you simply don't have to use unset() to avoid any sort of memory leaks associated with creating references? I'm using PHP 5.. btw. Unsetting references in PHP PHP references tutorial Here is the code - I'm creating references when I create $temp and $this-head at certain points in the LLL class: class Node { public $data; public $next; } class LLL { // The first node private $head; public function __construct() { $this->head = NULL; } public function insertFirst($data) { if (!$this->head) { // Create the head $this->head = new Node; $temp =& $this->head; $temp->data = $data; $temp->next = NULL; } else { // Add a node, and make it the new head. $temp = new Node; $temp->next = $this->head; $temp->data = $data; $this->head =& $temp; } } public function showAll() { echo "The linear linked list:<br/>&nbsp;&nbsp;"; if ($this->head) { $temp =& $this->head; do { echo $temp->data . " "; } while ($temp =& $temp->next); } else { echo "is empty."; } echo "<br/>"; } } Thanks!

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• Which MS technologies would be suited for a data intensive application?

  - by steve.tse

  I'm a junior VB.net developer with little application design knowledge. I've been reading a lot of material online regarding different design patterns, frameworks, and methodologies. It's become a bit confusing for me. Right now I'm trying to decide on what language would be best suited to convert an existing VB6 application (with SQL server backend.) I need to update the UI and add more user functionality and reporting capabilities. Initially I was thinking of using WPF and attempting the MVVM model for this big project. Reports would be generated from SSRS. A peer suggested using ASP.net and I don't have enough experience to determine what would be better. The senior programmers here are stuck on using VB6 and don't have any input on what to use. They are encouraging me to use the latest technologies. This application would be for ~20 users in a central location. Ideally I would stick to a Microsoft .net language. Current interface is similar to a datagrid table where the user would click in to see the detail of each record. They would need to have multiple records open at any given time. I look forward to all the advice I can get. EDIT 2010/04/22 2:47 PM EST What is your audience? Internal clients within an intranet How complex are the interactions you expect to implement? not very... displaying data from SQL server to UI. Allow user updates to said data. Typically just one user modifying a record. Do you require near real-time data updates? no How often do you expect to update the application after the first release? twice/year Do you expect a well-defined set of client platforms? Yes, windows xp environment, potentially upgrading to Win7. Currently in IE.6 moving to IE7 or 8 within a couple of months. Do users need access from anywhere? No, just from their PC.

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• 2 dimensional arraylists in java

  - by Chris Maness

  So here's the deal I'm working on a project that requires me to have a 2 dimensional arraylist of 1 dimensional arrays. But every time I try to load in my data I get an error: Can't do this opperation because of bad input java.lang.IndexOutOfBoundsException: Index: 1, Size: 0 On some of the inputs. I've got no idea where I'm going wrong on this one. A little help please? Source Code: import java.io.BufferedInputStream; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.util.ArrayList; import java.util.Scanner; import javax.swing.JOptionPane; import java.io.InputStream; public class Facebull { public static void main (String[] args) { if(args.length != 0){ load(args[0]); } else{ load("testFile"); } } public static void load(String fname) { int costOfMach = 0; ArrayList <Integer> finalMach = new ArrayList<Integer>(); ArrayList <ArrayList<int[]>>machines = new ArrayList<ArrayList<int[]>>(); Scanner inputFile = null; File f = new File(fname); if (f.exists ()) { try { inputFile = new Scanner (f); } catch (FileNotFoundException e) { JOptionPane.showMessageDialog(null,"Can't find the file\n" + e); } int i = 0; while (inputFile.hasNext ( )) { String str = inputFile.nextLine ( ); String [ ] fields = str.split ("[\t ]"); System.out.println(str); if (!(fields[0].isEmpty() || fields[0].equals (""))){ fields[0] = fields[0].substring(1); fields[1] = fields[1].substring(1); fields[2] = fields[2].substring(1); try { //data to be inputed is 0 and 3 location of data is 1 and 2 int[] item = new int[2]; item[1] = Integer.parseInt(fields[0]); item[0] = Integer.parseInt(fields[3]); if(machines.size() < Integer.parseInt(fields[1])){ ArrayList<int[]> column = new ArrayList<int[]>(); machines.add (Integer.parseInt(fields[1])-1, column); System.out.println("we're in the if"); } machines.get(Integer.parseInt(fields[1])-1).add(Integer.parseInt(fields[2])-1, item); } //catches any exception catch (Exception e) { System.out.println("Can't do this opperation because of bad input \n" + e); } } } inputFile.close ( ); } System.out.print(machines); }//end load }

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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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• Can I use WCF to replace my current Web Service and Window Service combination?

  - by gun_shy

  I need a little bit of advise regarding the situation I am faced with. The current arrangement I have been tasked with improving just doesn't sit well with me and I feel like there is a better way to do it. The more I read about WCF, the more I get the feeling that it might be what I am looking for. Right now, I have an asp.net client, a .net web service, a windows service, a ms sql database, and a third party application that is used for processing a group of 'project' files into a finalized file. Since the third party application can only handle processing one 'project' at a time, the combination of the web service, window service, and database have been arranged to create a job queue manager for the third party application. The client sends a zip 'project' file containing multiple sub files to the web service. The web service adds a new 'project' line to the database, generating a unique job id. The zip file is expanded to a folder location on the server using the job id as the folder name. The web service then returns the job id to the client. The client will use this id to poll the web service for the status of the job submitted. When the job is complete, the client will request the processed file. The windows service polls the database every x minutes. If a new job exists, the service will pull the oldest job and send it to the third party app for processing. If the processing succeeds, the window service updates the project line in the database, marking the job complete. The window service will continue to process any non complete jobs in the database until there are no more. When it stops finding any jobs, it will sleep x minutes and then poll the database again. I do not like the fact that the window service has to poll the database. If there is only one job submitted, the client will have to wait for the window service to poll and then wait while the 'project' is being processed. It seems like WCF could be used to combine the web and window services using a combination of the InstanceContextMode.Single and ConcurrencyMode.Multiple. So far, I have been unable to find any articles or examples that would point me in the right direction. Can WCF be utilized to accomplish the job queue logic of the current arrangement in a better way? As always, any help is more than appreciated.

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• I need to modify a program to use arrays and a method call. Should I modify the running file, the data collection file, or both?

  - by g3n3rallyl0st

  I have to have multiple classes for this program. The problem is, I don't fully understand arrays and how they work, so I'm a little lost. I will post my program I have written thus far so you can see what I'm working with, but I don't expect anyone to DO my assignment for me. I just need to know where to start and I'll try to go from there. I think I need to use a double array since I will be working with decimals since it deals with money, and my method call needs to calculate total price for all items entered by the user. Please help: RUNNING FILE package inventory2; import java.util.Scanner; public class RunApp { public static void main(String[] args) { Scanner input = new Scanner( System.in ); DataCollection theProduct = new DataCollection(); String Name = ""; double pNumber = 0.0; double Units = 0.0; double Price = 0.0; while(true) { System.out.print("Enter Product Name: "); Name = input.next(); theProduct.setName(Name); if (Name.equalsIgnoreCase("stop")) { return; } System.out.print("Enter Product Number: "); pNumber = input.nextDouble(); theProduct.setpNumber(pNumber); System.out.print("Enter How Many Units in Stock: "); Units = input.nextDouble(); theProduct.setUnits(Units); System.out.print("Enter Price Per Unit: "); Price = input.nextDouble(); theProduct.setPrice(Price); System.out.print("\n Product Name: " + theProduct.getName()); System.out.print("\n Product Number: " + theProduct.getpNumber()); System.out.print("\n Amount of Units in Stock: " + theProduct.getUnits()); System.out.print("\n Price per Unit: " + theProduct.getPrice() + "\n\n"); System.out.printf("\n Total cost for %s in stock: $%.2f\n\n\n", theProduct.getName(), theProduct.calculatePrice()); } } } DATA COLLECTION FILE package inventory2; public class DataCollection { String productName; double productNumber, unitsInStock, unitPrice, totalPrice; public DataCollection() { productName = ""; productNumber = 0.0; unitsInStock = 0.0; unitPrice = 0.0; } //setter methods public void setName(String name) { productName = name; } public void setpNumber(double pNumber) { productNumber = pNumber; } public void setUnits(double units) { unitsInStock = units; } public void setPrice(double price) { unitPrice = price; } //getter methods public String getName() { return productName; } public double getpNumber() { return productNumber; } public double getUnits() { return unitsInStock; } public double getPrice() { return unitPrice; } public double calculatePrice() { return (unitsInStock * unitPrice); } }

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• pagerAnchorBuilder - trying to add classes

  - by Bert Murphy

  I'm using Cycle2 to build a carousel gallery and I've run into a little problem regarding styling the pager buttons. What I've gathered is that Cycle2 creates its own pager span tags for each slide which is a bummer becaus I've already styled my the sub-nav markup. This should be a minor issue as long as I can assign individual classes to the spans and change my css accordingly. However, I can't get this to work. TLDR: I was hoping that I could use pagerAnchorBuilder to create individual classes for each span. I can't. Help. The original markup (pre Cycle2) looks like the following: <div id ="sub-nav" class="sub-nav"> <ul> <li><a id="available" class="available" href="#"></a></li> <li><a id="reliable" class="reliable" href="#"></a></li> <li><a id="use" class="use" href="#"></a></li> <li><a id="reports" class="reports" href="#"></a></li> <li class="last"><a id="software" class="software" href="#"></a></li> </ul> </div> With Cycle2 it looks like this (note the addition of the span tags) <div id ="sub-nav" class="sub-nav"> <ul> <li><a id="available" class="available" href="#"></a></li> <li><a id="reliable" class="reliable" href="#"></a></li> <li><a id="use" class="use" href="#"></a></li> <li><a id="reports" class="reports" href="#"></a></li> <li class="last"><a id="software" class="software" href="#"></a></li> </ul> <span class="cycle-pager-active">•</span><span>•</span><span>•</span><span>•</span><span>•</span></nav> </div> Cycle2 $('#sliding-gallery ul').cycle({ fx: 'carousel', carouselVisible: 1, speed: 'fast', timeout: 10000, slides: '>li', next: '.next', prev: '.prev', pager: '.sub-nav', pagerAnchorBuilder: function(idx, slide) { return '.sub-nav span:eq(' + idx + ')'; } });

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• SQL Design Question regarding schema and if Name value pair is the best solution

  - by Aur

  I am having a small problem trying to decide on database schema for a current project. I am by no means a DBA. The application parses through a file based on user input and enters that data in the database. The number of fields that can be parsed is between 1 and 42 at the current moment. The current design of the database is entirely flat with there being 42 columns; some have repeated columns such as address1, address2, address3, etc... This says that I should normalize the data. However, data integrity is not needed at this moment and the way the data is shaped I'm looking at several joins. Not a bad thing but the data is still in a 1 to 1 relationship and I still see a lot of empty fields per row. So my concerns are that this does not allow the database or the application to be very extendable. If they want to add more fields to be parsed (which they do) than I'd need to create another table and add another foreign key to the linking table. The third option is I have a table where the fields are defined and a table for each record. So what I was thinking is to make a table that stores the value and then links to those two tables. The problem is I can picture the size of that table growing large depending on the input size. If someone gives me a file with 300,000 records than 300,000 x 40 = 12 million so I have some reservations. However I think if I get to that point than I should be happy it is being used. This option also allows for more custom displaying of information albeit a bit more work but little rework even if you add more fields. So the problem boils down to: 1. Current design is a flat file which makes extending it hard and it is not normalized. 2. Normalize the tables although no real benefits for the moment but requirements change. 3. Normalize it down into the name value pair and hope size doesn't hurt. There are a large number of inserts, updates, and selects against that table. So performance is a worry but I believe the saying is design now, performance testing later? I'm probably just missing something practical so any comments would be appreciated even if it’s a quick sanity check. Thank you for your time.

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• Large transactions causing "System.Data.SqlClient.SqlException: Timeout expired" error?

  - by Michael

  My application requires a user to log in and allows them to edit a list of things. However, it seems that if the same user always logs in and out and edits the list, this user will run into a "System.Data.SqlClient.SqlException: Timeout expired." error. I've read comments about increasing the timeout period but I've also read a comment about it possibly caused by uncommitted transactions. And I do have one going in the application. I'll provide the code I'm working with and there is an IF statement in there that I was a little iffy about but it seemed like a reasonable thing to do. I'll just go over what's going on here, there is a list of objects to update or add into the database. New objects created in the application are given an ID of 0 while existing objects have their own ID's generated from the DB. If the user chooses to delete some objects, their IDs are stored in a separate list of Integers. Once the user is ready to save their changes, the two lists are passed into this method. By use of the IF statement, objects with ID of 0 are added (using the Add stored procedure) and those objects with non-zero IDs are updated (using the Update stored procedure). After all this, a FOR loop goes through all the integers in the "removal" list and uses the Delete stored procedure to remove them. A transaction is used for all this. Public Shared Sub UpdateSomethings(ByVal SomethingList As List(Of Something), ByVal RemovalList As List(Of Integer)) Using DBConnection As New SqlConnection(conn) DBConnection.Open() Dim MyTransaction As SqlTransaction MyTransaction = DBConnection.BeginTransaction() Try For Each SomethingItem As Something In SomethingList Using MyCommand As New SqlCommand() MyCommand.Connection = DBConnection If SomethingItem.ID > 0 Then MyCommand.CommandText = "UpdateSomething" Else MyCommand.CommandText = "AddSomething" End If MyCommand.Transaction = MyTransaction MyCommand.CommandType = CommandType.StoredProcedure With MyCommand.Parameters If MyCommand.CommandText = "UpdateSomething" Then .Add("@id", SqlDbType.Int).Value = SomethingItem.ID End If .Add("@stuff", SqlDbType.Varchar).Value = SomethingItem.Stuff End With MyCommand.ExecuteNonQuery() End Using Next For Each ID As Integer In RemovalList Using MyCommand As New SqlCommand("DeleteSomething", DBConnection) MyCommand.Transaction = MyTransaction MyCommand.CommandType = CommandType.StoredProcedure With MyCommand.Parameters .Add("@id", SqlDbType.Int).Value = ID End With MyCommand.ExecuteNonQuery() End Using Next MyTransaction.Commit() Catch ex As Exception MyTransaction.Rollback() 'Exception handling goes here End Try End Using End Sub There are three stored procedures used here as well as some looping so I can see how something can be holding everything up if the list is large enough. Other users can log in to the system at the same time just fine though. I'm using Visual Studio 2008 to debug and am using SQL Server 2000 for the DB.

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• C# - periodic data reading and Thread.Sleep()

  - by CaldonCZE

  Hello, my C# application reads data from special USB device. The data are read as so-called "messages", each of them having 24 bytes. The amount of messages that must be read per second may differ (maximal frequency is quite high, about 700 messages per second), but the application must read them all. The only way to read the messages is by calling function "ReadMessage", that returns one message read from the device. The function is from external DLL and I cannot modify it. My solution: I've got a seperate thread, that is running all the time during the program run and it's only job is to read the messages in cycle. The received messages are then processed in main application thread. The function executed in the "reading thread" is the following: private void ReadingThreadFunction() { int cycleCount; try { while (this.keepReceivingMessages) { cycleCount++; TRxMsg receivedMessage; ReadMessage(devHandle, out receivedMessage); //...do something with the message... } } catch { //... catch exception if reading failed... } } This solution works fine and all messages are correctly received. However, the application consumes too much resources, the CPU of my computer runs at more than 80%. Therefore I'd like to reduce it. Thanks to the "cycleCount" variable I know that the "cycling speed" of the thread is about 40 000 cycles per second. This is unnecessarily too much, since I need to receive maximum 700 messagges/sec. (and the device has buffer for about 100 messages, so the cycle speed can be even a little lower) I tried to reduce the cycle speed by suspending the thread for 1 ms by Thread.Sleep(1); command. Of course, this didn't work and the cycle speed became about 70 cycles/second which was not enough to read all messages. I know that this attempt was silly, that putting the thread to sleep and then waking him up takes much longer than 1 ms. However, I don't know what else to do: Is there some other way how to slow the thread execution down (to reduce CPU consumption) other than Thread.Sleep? Or am I completely wrong and should I use something different for this task instead of Thread, maybe Threading.Timer or ThreadPool? Thanks a lot in advance for all suggestions. This is my first question here and I'm a beginner at using threads, so please excuse me if it's not clear enough.

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• XSLT 2.0 Header Leaks into Transformed XML

  - by user1303797

  First, a thank you in advance. Second, this is my first post so apologies for any errors or wrongdoings. I am a noob w/ xml and xslt, and can't seem to figure this out. When I transform some xml using xslt 2.0, some of the headers from the xslt leaks into the new xml. It doesn't seem to do it in xslt 1.0 (granted the xslt is a little different). Here is the xml: <?xml version="1.0" encoding="ISO-8859-1" ?> <xml_content> <feed_name>feed</feed_name> <feed_info> <entry_1> <id>1</id> <pub_date>1320814800</pub_date> </entry_1> </feed_info> </xml_content> Here is the xslt: <xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="http://www.w3.org/TR/xhtml1/strict"> <xsl:output method="xml" indent="yes" /> <xsl:template match="xml_content"> <Records> <xsl:for-each select="feed_info/entry_1"> <Record> <ID><xsl:value-of select="id" /></ID> <PublicationDate><xsl:value-of select='xs:dateTime("1970-01-01T00:00:00") + xs:integer(pub_date) * xs:dayTimeDuration("PT1S")'/></PublicationDate> </Record> </xsl:for-each> </Records> </xsl:template> </xsl:stylesheet> Here is the new xml. Look specifically at the first "Records" element. <?xml version="1.0" encoding="UTF-8"?> <Records xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="http://www.w3.org/TR/xhtml1/strict"> <Record> <ID>1</ID> <PublicationDate>2011-11-09T05:00:00</PublicationDate> </Record> </Records>

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• Is it possible to create a C++ factory system that can create an instance of any "registered" object

  - by chrensli

  Hello, I've spent my entire day researching this topic, so it is with some scattered knowledge on the topic that i come to you with this inquiry. Please allow me to describe what I am attempting to accomplish, and maybe you can either suggest a solution to the immediate question, or another way to tackle the problem entirely. I am trying to mimic something related to how XAML files work in WPF, where you are essentially instantiating an object tree from an XML definition. If this is incorrect, please inform. This issue is otherwise unrelated to WPF, C#, or anything managed - I solely mention it because it is a similar concept.. So, I've created an XML parser class already, and generated a node tree based on ObjectNode objects. ObjectNode objects hold a string value called type, and they have an std::vector of child ObjectNode objects. The next step is to instantiate a tree of objects based on the data in the ObjectNode tree. This intermediate ObjectNode tree is needed because the same ObjectNode tree might be instantiated multiple times or delayed as needed. The tree of objects that is being created is such that the nodes in the tree are descendants of a common base class, which for now we can refer to as MyBase. Leaf nodes can be of any type, not necessarily derived from MyBase. To make this more challenging, I will not know what types of MyBase derived objects might be involved, so I need to allow for new types to be registered with the factory. I am aware of boost's factory. Their docs have an interesting little design paragraph on this page: o We may want a factory that takes some arguments that are forwarded to the constructor, o we will probably want to use smart pointers, o we may want several member functions to create different kinds of objects, o we might not necessarily need a polymorphic base class for the objects, o as we will see, we do not need a factory base class at all, o we might want to just call the constructor - without #new# to create an object on the stack, and o finally we might want to use customized memory management. I might not be understanding this all correctly, but that seems to state that what I'm trying to do can be accomplished with boost's factory. But all the examples I've located, seem to describe factories where all objects are derived from a base type. Any guidance on this would be greatly appreciated. Thanks for your time!

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• How can I obtain the IPv4 address of the client?

  - by Dr Dork

  Hello! I'm prepping for a simple work project and am trying to familiarize myself with the basics of socket programming in a Unix dev environment. At this point, I have some basic server side code setup to listen for incoming TCP connection requests from clients after the parent socket has been created and is set to listen... int sockfd, newfd; unsigned int len; socklen_t sin_size; char msg[]="Test message sent"; char buf[MAXLEN]; int st, rv; struct addrinfo hints, *serverinfo, *p; struct sockaddr_storage client; char ip[INET6_ADDRSTRLEN]; . . //parent socket creation and listen code omitted for simplicity . //wait for connection requests from clients while(1) { //Returns the socketID and address of client connecting to socket if( ( newfd = accept(sockfd, (struct sockaddr *)&client, &len) ) == -1 ){ perror("Accept"); exit(-1); } if( (rv = recv(newfd, buf, MAXLEN-1, 0 )) == -1) { perror("Recv"); exit(-1); } struct sockaddr_in *clientAddr = ( struct sockaddr_in *) get_in_addr((struct sockaddr *)&client); inet_ntop(client.ss_family, clientAddr, ip, sizeof ip); printf("Receive from %s: query type is %s\n", ip, buf); if( ( st = send(newfd, msg, strlen(msg), 0)) == -1 ) { perror("Send"); exit(-1); } //ntohs is used to avoid big-endian and little endian compatibility issues printf("Send %d byte to port %d\n", ntohs(clientAddr->sin_port) ); close(newfd); } } I found the get_in_addr function online and placed it at the top of my code and use it to obtain the IP address of the client connecting... // get sockaddr, IPv4 or IPv6: void *get_in_addr(struct sockaddr *sa) { if (sa->sa_family == AF_INET) { return &(((struct sockaddr_in*)sa)->sin_addr); } return &(((struct sockaddr_in6*)sa)->sin6_addr); } but the function always returns the IPv6 IP address since thats what the sa_family property is set as. My question is, is the IPv4 IP address stored anywhere in the data I'm using and, if so, how can I access it? Thanks so much in advance for all your help!

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• Request URL in Javascript, Fetch URL Content using Java Applet, return to Javascript?

  - by Sam G

  I'm in the process of making a little experiment, it grabs a YouTube page, and returns the highest quality MP4 link, then plays this in a HTML 5 Video element. Now I was using PHP with cURL to get the URL content (YouTube), but that only works on my local server (MP4 link is locked to IP address). I can't think of any other way to get the page content due to cross domain rules except a Java applet. So I've built a Java applet that should return the content of a URL. Java import java.applet.Applet; import java.awt.*; import java.io.ByteArrayOutputStream; import java.io.InputStream; import java.net.HttpURLConnection; import java.net.URL; public class URLFetcherabc extends Applet { public void init() { } public void paint(Graphics g) { g.drawString("Java loaded. Waiting for URL", 0, 10); } public String getURL(String url, String httpMethod) { try { URL u = new URL(url); HttpURLConnection conn = (HttpURLConnection)u.openConnection(); conn.setRequestMethod(httpMethod); InputStream is = conn.getInputStream(); ByteArrayOutputStream output = new ByteArrayOutputStream(); byte[] buffer = new byte[1024]; for (int bytesRead = 0; (bytesRead = is.read(buffer)) != -1; ) { output.write(buffer, 0, bytesRead); } return output.toString(); } catch (Exception e) { }return null; } } Now I've got the applet on the page, but every-time I call the function it returns nothing. Heres my HTML for including the applet. HTML <applet id="URLFetcher" name="URLFetcher" code="URLFetcherabc.class" archive="URLFetcher.jar" height="200" width="200" mayscript=""></applet> Java-Script function fetchurl(urltofetch) { var URLFetcher = document.getElementById("URLFetcher"); var result = URLFetcher.getURL(urltofetch); //Result = URL Content return result; } The function always returns null, in Java the function does work when passed a variable via other means (parameter etc). I've tried running other functions through Javascript and the Java applet does respond. I'm new to Java applets and communicating with them via Javascript, so I'm probably making either a small mistake somewhere or its completely wrong. Any ideas? Thanks

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• How to create multiple Repository object inside a Repository class using Unit Of Work?

  - by Santosh

  I am newbie to MVC3 application development, currently, we need following Application technologies as requirement MVC3 framework IOC framework – Autofac to manage object creation dynamically Moq – Unit testing Entity Framework Repository and Unit Of Work Pattern of Model class I have gone through many article to explore an basic idea about the above points but still I am little bit confused on the “Repository and Unit Of Work Pattern “. Basically what I understand Unit Of Work is a pattern which will be followed along with Repository Pattern in order to share the single DB Context among all Repository object, So here is my design : IUnitOfWork.cs public interface IUnitOfWork : IDisposable { IPermitRepository Permit_Repository{ get; } IRebateRepository Rebate_Repository { get; } IBuildingTypeRepository BuildingType_Repository { get; } IEEProjectRepository EEProject_Repository { get; } IRebateLookupRepository RebateLookup_Repository { get; } IEEProjectTypeRepository EEProjectType_Repository { get; } void Save(); } UnitOfWork.cs public class UnitOfWork : IUnitOfWork { #region Private Members private readonly CEEPMSEntities context = new CEEPMSEntities(); private IPermitRepository permit_Repository; private IRebateRepository rebate_Repository; private IBuildingTypeRepository buildingType_Repository; private IEEProjectRepository eeProject_Repository; private IRebateLookupRepository rebateLookup_Repository; private IEEProjectTypeRepository eeProjectType_Repository; #endregion #region IUnitOfWork Implemenation public IPermitRepository Permit_Repository { get { if (this.permit_Repository == null) { this.permit_Repository = new PermitRepository(context); } return permit_Repository; } } public IRebateRepository Rebate_Repository { get { if (this.rebate_Repository == null) { this.rebate_Repository = new RebateRepository(context); } return rebate_Repository; } } } PermitRepository .cs public class PermitRepository : IPermitRepository { #region Private Members private CEEPMSEntities objectContext = null; private IObjectSet<Permit> objectSet = null; #endregion #region Constructors public PermitRepository() { } public PermitRepository(CEEPMSEntities _objectContext) { this.objectContext = _objectContext; this.objectSet = objectContext.CreateObjectSet<Permit>(); } #endregion public IEnumerable<RebateViewModel> GetRebatesByPermitId(int _permitId) { // need to implment } } PermitController .cs public class PermitController : Controller { #region Private Members IUnitOfWork CEEPMSContext = null; #endregion #region Constructors public PermitController(IUnitOfWork _CEEPMSContext) { if (_CEEPMSContext == null) { throw new ArgumentNullException("Object can not be null"); } CEEPMSContext = _CEEPMSContext; } #endregion } So here I am wondering how to generate a new Repository for example “TestRepository.cs” using same pattern where I can create more then one Repository object like RebateRepository rebateRepo = new RebateRepository () AddressRepository addressRepo = new AddressRepository() because , what ever Repository object I want to create I need an object of UnitOfWork first as implmented in the PermitController class. So if I would follow the same in each individual Repository class that would again break the priciple of Unit Of Work and create multiple instance of object context. So any idea or suggestion will be highly appreciated. Thank you

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• Newbie jQuery question: Need slideshow to rotate automatically, not just when clicking navigation.

  - by Justin

  Hi everyone, This is my first post, so please forgive me if this question has been asked a million times. I'm a self professed jQuery hack and I need a little guidance on taking this script I found and adapting it to my needs. Anyway, what I'm making is an image slide show with navigation. The script I found does this, but does not automatically cycle through the images. I'm using jQuery 1.3.2 and would rather stick with that than using the newer library. I would also prefer to edit what is already here rather than start from scratch. Anywho, here's the html: <div id="myslide"> <div class="cover"> <div class="mystuff"> <img alt="&nbsp;" src="http://www.mfhc.com/wp/wp-content/uploads/2010/05/current_Denver-skyline.jpg" /> </div> <div class="mystuff"> <img alt="&nbsp;" src="http://www.mfhc.com/wp/wp-content/uploads/2010/05/pepsi_center-IS42RF-0D111C.jpg" /> </div> <div class="mystuff"> <img alt="&nbsp;" src="http://www.mfhc.com/wp/wp-content/uploads/2010/05/columbine-2689820469_D1104.jpg" /> </div> <div class="mystuff"> <img alt="&nbsp;" src="http://www.mfhc.com/wp/wp-content/uploads/2010/05/ist2_10460354-RedRocks.jpg" /> </div> </div> <!-- end of div cover --> </div> <!-- end of div myslide --> And here's the jQuery: <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script> <script type="text/JavaScript"> $(document).ready(function (){ $('#button a').click(function(){ var integer = $(this).attr('rel'); $('#myslide .cover').css({left:-820*(parseInt(integer)-1)}).hide().fadeIn(); /*----- Width of div #mystuff (here 820) ------ */ $('#button a').each(function(){ $(this).removeClass('active'); if($(this).hasClass('button'+integer)){ $(this).addClass('active')} }); }); }); </script> Here's where I got the script: http://www.webdeveloperjuice.com/2010/04/07/create-lightweight-jquery-fade-manual-slideshow/ Again, if this question is too basic for this site please let me know and possibly provide a reference link or two. Thanks a ton!

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