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  • Laws of Computer Science and Programming

    - by Jonas
    We have Amdahl's law that basically states that if your program is 10% sequential you can get a maximum 10x performance boost by parallelizing your application. Another one is Wadler's law which states that In any language design, the total time spent discussing a feature in this list is proportional to two raised to the power of its position. 0. Semantics 1. Syntax 2. Lexical syntax 3. Lexical syntax of comments My question is this: What are the most important (or at least significant / funny but true / sad but true) laws of Computer Science and programming? I want named laws, and not random theorems, So an answer should look something like Surname's (law|theorem|conjecture|corollary...) Please state the law in your answer, and not only a link. Edit: The name of the law does not need to contain it's inventors surname. But I do want to know who stated (and perhaps proved) the law

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  • iPhone, No Garbage Collection: What About MonoTouch?

    - by yar
    It's well known that Apple does not provide automatic garbage collection on the iPhone to prolong battery life. Yet MonoTouch apps, which reportedly run perfectly on the iPhone (and many are sold through the AppStore, therefore are approved by Apple), do have automatic garbage collection. Is this automatic garbage collection, or does MonoTouch merely manage all the retain/release stuff for you? If it is automatic garbage collection, wouldn't that be a drain on battery? Edit: If your answer to #1 is "yes" and your answer to #2 is "no," why?

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  • HMAC SHA1 ColdFusion

    - by Chris
    Please help! I have been pulling out my hair over this one. :) I have a site that I need to HMAC SHA1 for authentication. It currently works with another language but now I need to move it to ColdFusion. For the life of me I cannot get the strings to match. Any assistance would be much appreciated. Data: https%3A%2F%2Fwww%2Etestwebsite%2Ecom%3Fid%3D5447 Key: 265D5C01D1B4C8FA28DC55C113B4D21005BB2B348859F674977B24E0F37C81B05FAE85FB75EA9CF53ABB9A174C59D98C7A61E2985026D2AA70AE4452A6E3F2F9 Correct answer: WJd%2BKxmFxGWdbw4xQJZXd3%2FHkFQ%3d My answer: knIVr6wIt6%2Fl7mBJPTTbwQoTIb8%3d Both are Base64 encoded and then URL encoded.

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  • Advice on logic circuits and serial communications

    - by Spencer Ruport
    As far as I understand the serial port so far, transferring data is done over pin 3. As shown here: There are two things that make me uncomfortable about this. The first is that it seems to imply that the two connected devices agree on a signal speed and the second is that even if they are configured to run at the same speed you run into possible synchronization issues... right? Such things can be handled I suppose but it seems like there must be a simpler method. What seems like a better approach to me would be to have one of the serial port pins send a pulse that indicates that the next bit is ready to be stored. So if we're hooking these pins up to a shift register we basically have: (some pulse pin)-clk, tx-d Is this a common practice? Is there some reason not to do this? EDIT Mike shouldn't have deleted his answer. This I2C (2 pin serial) approach seems fairly close to what I did. The serial port doesn't have a clock you're right nobugz but that's basically what I've done. See here: private void SendBytes(byte[] data) { int baudRate = 0; int byteToSend = 0; int bitToSend = 0; byte bitmask = 0; byte[] trigger = new byte[1]; trigger[0] = 0; SerialPort p; try { p = new SerialPort(cmbPorts.Text); } catch { return; } if (!int.TryParse(txtBaudRate.Text, out baudRate)) return; if (baudRate < 100) return; p.BaudRate = baudRate; for (int index = 0; index < data.Length * 8; index++) { byteToSend = (int)(index / 8); bitToSend = index - (byteToSend * 8); bitmask = (byte)System.Math.Pow(2, bitToSend); p.Open(); p.Parity = Parity.Space; p.RtsEnable = (byte)(data[byteToSend] & bitmask) > 0; s = p.BaseStream; s.WriteByte(trigger[0]); p.Close(); } } Before anyone tells me how ugly this is or how I'm destroying my transfer speeds my quick answer is I don't care about that. My point is this seems much much simpler than the method you described in your answer nobugz. And it wouldn't be as ugly if the .Net SerialPort class gave me more control over the pin signals. Are there other serial port APIs that do?

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  • How to fake source ip-address of a udp-packet?

    - by youllknow
    Hi everyone! Think about the following: Your ISP offers you a dynamic ip-address (for example 123.123.123.123). My question is simple (the answer may not): Is it possible to send a single udp-packet with a outer source-ip (for example 124.124.124.124) to a fixed-ip server? I don't need to get a answer from the server. I just want to know if/how this one way communication can be done, using a faked source-ip address. I'm sorry for my bad English! Thanks for you help in advance!

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  • tips for learning from opensource

    - by dole doug
    Hi there, Besides practice(practice and more practice) reading books and forums, analyzing others people code is a must in order to have a career in this field. The problem is that I'm a student(feels like always on learning stage) but sometimes i can't solve the problems by my own. I was thinking that on public open source repositories might be the answer I'm looking for. My question is how can i find the answer to some of my problems in open source projects/community? Do you have any tips to share for me? ty

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  • ASP.NET Binding integer to CheckBox's Checked field

    - by Sung Meister
    I have a following ListView item template, in which I am trying to bind integer value to Checked property of CheckBox. IsUploaded value contains only 0 and 1... <asp:ListView ID="trustListView" runat="server"> <ItemTemplate> <asp:CheckBox ID="isUploadedCheckBox" runat="server" Checked='<%# Bind("IsUploaded") %>' /> </ItemTemplate> </asp:ListView> But ASP.NET complains that Exception Details: System.InvalidCastException: Sepcified cast is not valid Even though following code using DataBinder.Eval() works, I need to have a 2-way binding, thus need to use Bind(). <asp:CheckBox ID="isUploadedCheckBox2" runat="server" Checked='<%# Convert.ToBoolean( DataBinder.Eval(Container.DataItem, "IsUploaded"))) %>' /> How can I convert 0's and 1's to boolean using Bind()? [ANSWER] I have extended auto-generated type through partial class by adding a new property mentioned in the answer by Justin

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  • What is a NullReferenceException in .NET?

    - by John Saunders
    (I'm creating this separate question and answer because every question we get on NullReferenceException is really the same) I have some code and when it executes, it throws a NullReferenceException, saying, "Object reference not set to an instance of an object.". What does this mean, and what can I do about it? Note again, that this is a question meant to focus answers to the canonical "what is a NullReferenceException and why did I get one" question. I do know what a NullReferenceException is, as my answer below demonstrates.

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  • How should I go about creating a point system for users like SO and yahoo answers?(PHP)

    - by ggfan
    I am creating a voting system for a Q&A site project in which if a user asks a question, he/she losses -5 points; answer a question +5, vote a question +1, etc. (kind of like SO and yahoo answers) --To create the basic arithmetic, I have a "users_points" table that relates the user_id and their total points. +---+---------+ | 1 | 100 | +---+---------+ | 2 | 54 | +---+---------+ --Basically if the users does certain task, it would + or - the points. How do I prevent users from say voting an answer up 100 times. ex: I want a user to be only able to vote once per question, etc.

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  • Kill a 10 minute old zombie process in linux bash script

    - by Steve
    I've been tinkering with a regex answer by yukondude with little success. I'm trying to kill processes that are older than 10 minutes. I already know what the process IDs are. I'm looping over an array every 10 min to see if any lingering procs are around and need to be killed. Anybody have any quick thoughts on this? Thanks, Steve ps -eo uid,pid,etime 3233332 | egrep ' ([0-9]+-)?([0-9]{2}:?){3}' | awk '{print $2}' | xargs -I{} kill {} I've been tinkering with the answer posted by yukondude with little success. I'm trying to kill processes that are older than 10 minutes. I already know what the process IDs are. I'm looping over an array every 10 min to see if any lingering procs are around and need to be killed. Anybody have any quick thoughts on this? Thanks, Steve

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  • C# ASP.Net The type or namespace name 'Secure' does not exist in the namespace 'source_extranet'

    - by Louis Russell
    Afternoon all, I really need your help as this is a Nightmare! I was earlier having a problem with referencing a 3rd Party Dll (Here) but have overcome this problem and am now having a problem referencing my own classes! Everything seems fine at build with no errors at all but when I go to run the application it comes up with the following Compilation Error: Compiler Error Message: CS0234: The type or namespace name 'Secure' does not exist in the namespace 'source_extranet' (are you missing an assembly reference?) The line that the Error points to this line in the class: source_extranet.Secure.BackendCustomData newdata = new source_extranet.Secure.BackendCustomData(); This line of code points to a class in the same folder as the calling code class. I have scoured Google looking for an answer and haven't found anything that points me to an answer to my problem. Any help would be AMAZING!

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  • PHP will not delete from MySQL

    - by Michal Kopanski
    For some reason, JavaScript/PHP wont delete my data from MySQL! Here is the rundown of the problem. I have an array that displays all my MySQL entries in a nice format, with a button to delete the entry for each one individually. It looks like this: <?php include("login.php"); //connection to the database $dbhandle = mysql_connect($hostname, $username, $password) or die("<br/><h1>Unable to connect to MySQL, please contact support at [email protected]</h1>"); //select a database to work with $selected = mysql_select_db($dbname, $dbhandle) or die("Could not select database."); //execute the SQL query and return records if (!$result = mysql_query("SELECT `id`, `url` FROM `videos`")) echo 'mysql error: '.mysql_error(); //fetch tha data from the database while ($row = mysql_fetch_array($result)) { ?> <div class="video"><a class="<?php echo $row{'id'}; ?>" href="http://www.youtube.com/watch?v=<?php echo $row{'url'}; ?>">http://www.youtube.com/watch?v=<?php echo $row{'url'}; ?></a><a class="del" href="javascript:confirmation(<? echo $row['id']; ?>)">delete</a></div> <?php } //close the connection mysql_close($dbhandle); ?> The delete button has an href of javascript:confirmation(<? echo $row['id']; ?>) , so once you click on delete, it runs this: <script type="text/javascript"> <!-- function confirmation(ID) { var answer = confirm("Are you sure you want to delete this video?") if (answer){ alert("Entry Deleted") window.location = "delete.php?id="+ID; } else{ alert("No action taken") } } //--> </script> The JavaScript should theoretically pass the 'ID' onto the page delete.php. That page looks like this (and I think this is where the problem is): <?php include ("login.php"); mysql_connect($hostname, $username, $password) or die("Unable to connect to MySQL"); mysql_select_db ($dbname) or die("Unable to connect to database"); mysql_query("DELETE FROM `videos` WHERE `videos`.`id` ='.$id.'"); echo ("Video has been deleted."); ?> If there's anyone out there that may know the answer to this, I would greatly appreciate it. I am also opened to suggestions (for those who aren't sure). Thanks!

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  • Can you find a pattern to sync files knowing only dates and filenames?

    - by Robert MacLean
    Imagine if you will a operating system that had the following methods for files Create File: Creates (writes) a new file to disk. Calling this if a file exists causes a fault. Update File: Updates an existing file. Call this if a file doesn't exist causes a fault. Read File: Reads data from a file. Enumerate files: Gets all files in a folder. Files themselves in this operating system only have the following meta data: Created Time: The original date and time the file was created, by the Create File method. Modified Time: The date and time the file was last modified by the Update File method. If the file has never been modified, this will equal the Create Time. You have been given the task of writing an application which will sync the files between two directories (lets call them bill and ted) on a machine. However it is not that simple, the client has required that The application never faults (see methods above). That while the application is running the users can add and update files and those will be sync'd next time the application runs. Files can be added to either the ted or bill directories. File names cannot be altered. The application will perform one sync per time it is run. The application must be almost entirely in memory, in other words you cannot create a log of filenames and write that to disk and then check that the next time. The exception to point 6 is that you can store date and times between runs. Each date/time is associated with a key labeled A through J (so you have 10 to use) so you can compare keys between runs. There is no way to catch exceptions in the application. Answer will be accepted based on the following conditions: First answer to meet all requirements will be accepted. If there is no way to meet all requirements, the answer which ensures the smallest amount of missed changes per sync will be accepted. A bounty will be created (100 points) as soon as possible for the prize. The winner will be selected one day before the bounty ends. Please ask questions in the comments and I will gladly update and refine the question on those.

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  • Why use MVVM???

    - by LnDCobra
    Okay, I have been looking into MVVM pattern, and each time I have previously tried looking into it, I gave up for a number of reasons: Unnecessary Extra Long Winded Coding No apparent advantages for coders (no designers in my office. Currently only myself soon to be another coder) Not a lot of resources/documentation of good practices! (Or at least hard to find) Cannot think of a single scenario where this is advantageous. I'm about to give up on it yet again, and thought I'd ask to see if someone answer the reasons above. I honestly can't see an advantage of using this for a single/partner coding. Even in complex projects with 10's of windows. To me the DataSet is a good enough view and binding like in the answer by Brent following question

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  • How to find two most distant points?

    - by depesz
    This is a question that I was asked on a job interview some time ago. And I still can't figure out sensible answer. Question is: you are given set of points (x,y). Find 2 most distant points. Distant from each other. For example, for points: (0,0), (1,1), (-8, 5) - the most distant are: (1,1) and (-8,5) because the distance between them is larger from both (0,0)-(1,1) and (0,0)-(-8,5). The obvious approach is to calculate all distances between all points, and find maximum. The problem is that it is O(n^2), which makes it prohibitively expensive for large datasets. There is approach with first tracking points that are on the boundary, and then calculating distances for them, on the premise that there will be less points on boundary than "inside", but it's still expensive, and will fail in worst case scenario. Tried to search the web, but didn't find any sensible answer - although this might be simply my lack of search skills.

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  • File size and mime-type before upload

    - by Marcos Placona
    Hi, I've scavenged on every single topic on this forum to try and find an answer before I posted this. Most people say you should simply use SWFUpload, some others mention Activex, and it keeps going. I know this is do-able, as Google does it with gMail when you try to upload a file that's bigger than 25mb, or executable. My question is, how can I determine the file size and mime-type before the file actually hits my server. I primarily thought it was an impossible task, but Google proves me wrong. Could anyone give me a definitive answer on how to accomplish such task? Thanks

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  • Eclipse RCP: Actions vs Commands - would like an update

    - by nEm
    I know this question has been asked before but it was in 2009 and I haven't found anything more recent either on the web. I was wondering if the answer in that still holds or can it be updated? I am just starting work on an RCP and I haven't been able to decide between actions and commands for my menu items. I will be using a lot of the ones provided by Eclipse such as the Edit, File and some of their sub menu items as well. Since it has been nearly two years for the answer provided in the '09 question, I just wanted to make sure there is nothing else that could sway my decision in either direction or maybe if there have been some new developments that I am not aware of.

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  • Dealing with UIImagePickerController to minimize memory useage

    - by Gordon Fontenot
    So, I have read the SO post on UIImagePickerController, UIImage, Memory and More, and I read the post on Memory Leak Problems with UIImagePickerController in iPhone. I have VASTLY increased my memory efficiency between these 2 posts, and I thank the OPs and the people that provided the answers. I just had a question on the answer provided in the Memory Leak question, which was (essentially): only have one instance of the controller throughout the programs runtime What would be the best way to go about this without causing memory leaks? Right now I am initiating it and releasing it on every use from within the view, and I am seeing exactly what the answer describes (Memory warnings and a crash after about 20 uses). Should I initiate the UIImagePickerController when I need it, but use a seperate class unrelated to the view to control it? How should I deal with releasing the controller if I do it this way?

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  • C# Training Quizzes

    - by John Sheppard
    Hello there, I have been programming 10 years, mostly in vba and vb.net but I know c# well enough to program what I normally do. I yesterday was applying for a Senior c# position and I did so poorly on the induction test its not funny :) I have always found that for me the best way to learn and recall is via question's and answers (multichoice and short answer). That is, a question is posed and after I answer instant feedback is given as to whether I choose right or wrong and the reasons why. As such I was wondering if anyone knew of or could recommend a C# quiz website. Something like a daily c# quiz to keep my brain up to date and fresh if I'm not always programming in it. Not something wimpy either. Something that does everything. Paying is not an obstacle, id prefer to pay for a good resource than muck around. Thank you

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  • What happens when you run out of ram with mlockall set?

    - by James Dean
    I am working on a C++ application that requires a large amounts of memory for a batch run. ( 20gb) Some of my customers are running into memory limits where sometimes the OS starts swapping and the total run time doubles or worse. I have read that I can use the mlockall to keep the process from being swapped out. What would happen when the process memory requirements approaches or exceeds the the available physical memory in this way? I guess the answer might be OS specific so please list the OS in your answer.

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  • Printing an array in a method, from a different class?

    - by O.Lodhi
    Hello All, I'm a fairly inexperienced programmer, and i'm currently working on a Console Application project. It's basically a little 'mathematics game'; the application generates two random numbers, that have either been added, subtracted, multiplied or divided against each other randomly. The answer is shown on screen and the user has to pick from the menu which is the right mathematical operator, once the correct answer is picked the application then displays on screen how long it took for the user in milliseconds to input the correct answer. Now I want to save the times of the players in an array that can be called up later with all the scores. I need to include a method in this programme and I figured a method to save the times into an array would be suitable. I seem to have stumbled across a little problem though. I'm not quite sure what's wrong: using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Mathgame { class Program { } class arrayclass { public static void saveInArray(int duration) { int[] TopTenScores = {000,1000,2000,3000,4000,5000,6000,7000,8000,9000}; if (duration < 1000) { duration = TopTenScores[000]; } else if ((duration >= 1000) && (duration <= 1999)) { duration = TopTenScores[1000]; } else if ((duration >= 2000) && (duration <= 2999)) { duration = TopTenScores[2000]; } else if ((duration >= 3000) && (duration <= 3999)) { duration = TopTenScores[3000]; } else if ((duration >= 4000) && (duration <= 4999)) { duration = TopTenScores[4000]; } else if ((duration >= 5000) && (duration <= 5999)) { duration = TopTenScores[5000]; } else if ((duration >= 6000) && (duration <= 6999)) { duration = TopTenScores[6000]; } else if ((duration >= 7000) && (duration <= 7999)) { duration = TopTenScores[7000]; } else if ((duration >= 8000) && (duration <= 8999)) { duration = TopTenScores[8000]; } else if ((duration >= 9000) && (duration <= 9999)) { duration = TopTenScores[9000]; } Console.WriteLine(TopTenScores); } static void Main(string[] args) { int intInput, num1, num2, incorrect, array1; float answer; string input; System.Random randNum = new System.Random(); Console.WriteLine("Welcome to the Maths game!"); Console.WriteLine("(Apologies for the glitchiness!)"); Console.WriteLine(); Console.WriteLine("Please choose from the following options:"); Console.WriteLine(); retry: Console.WriteLine("1 - Test your Maths against the clock!"); Console.WriteLine("2 - Exit the application."); Console.WriteLine("3 - Top scores"); Console.WriteLine(); input = Console.ReadLine(); intInput = int.Parse(input); if (intInput == 1) { goto start; } else if (intInput == 2) { goto fin; } else if (intInput == 3) { array1 = array1.saveInArray; goto retry; } Now, in the last 'else if' statement in the code, you can see my variable array1 trying to call the method, but no matter what I do I keep getting errors. This is the only error I have at the moment, but I have a feeling soon as I resolve that error, another will come up. For now i'm just determined to get past this error: 'int' does not contain a definition for 'saveInArray' and no extension method 'saveInArray' accepting a first argument of type 'int' could be found (are you missing a using directive or an assembly reference?). Any help would be kindly appreciated, apologies in advanced for my ugly written code! And thank you to any help that I receive! Regards, Omar.

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  • GAE datastore eager loading in python api

    - by tomus
    I have two models in relation one-to-many: class Question(db.Model): questionText = db.StringProperty(multiline=False) class Answer(db.Model): answerText = db.StringProperty(multiline=False) question = db.ReferenceProperty(Question, collection_name='answers') I have front-end implemented in Flex and use pyamf to load data. When i try to load all answers with related questions all works as desired and I can access field answer.question however in case of loading questions (e.g. by Questions.all() ), 'question.answers' remains empty/null (though on server/python side I can revise question.answers without problem - probably after lazy-loading). So is it possible to load all questions along with answers ? (I know this is possible in JPA Java api but what about python ?) Shoud I use additional setting, GQL query or django framework to make it work ?

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  • Is it posible for WIndows Speech Recognition Engine to use in my project like word pronounciation ga

    - by XBasic3000
    I use to create an application that uses the windows speech recognition engine or the SAPI. its like a game for pronounciation that it give you score when you pronounce it correctly. but when i started experiments with SAPI, it has poor recognition unless if you load a grammar on it (XML) its give best recognition result. but the problem now is closest pronounciation from the input text will be recognize. for example: Database - dedebase - correct. even if you mispronounce it. it gives you correct answers. without using the xml grammar when you say database it give you "in the base/the base/data base/etc..." please post your answer,suggestion,clarication and please votes for best answer.

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