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• Are endless loops in bad form?

  - by rlbond

  So I have some C++ code for back-tracking nodes in a BFS algorithm. It looks a little like this: typedef std::map<int> MapType; bool IsValuePresent(const MapType& myMap, int beginVal, int searchVal) { int current_val = beginVal; while (true) { if (current_val == searchVal) return true; MapType::iterator it = myMap.find(current_val); assert(current_val != myMap.end()); if (current_val == it->second) // end of the line return false; current_val = it->second; } } However, the while (true) seems... suspicious to me. I know this code works, and logically I know it should work. However, I can't shake the feeling that there should be some condition in the while, but really the only possible one is to use a bool variable just to say if it's done. Should I stop worrying? Or is this really bad form. EDIT: Thanks to all for noticing that there is a way to get around this. However, I would still like to know if there are other valid cases.

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• Deploying software on compromised machines

  - by Martin

  I've been involved in a discussion about how to build internet voting software for a general election. We've reached a general consensus that there exist plenty of secure methods for two way authentication and communication. However, someone came along and pointed out that in a general election some of the machines being used are almost certainly going to be compromised. To quote: Let me be an evil electoral fraudster. I want to sample peoples votes as they vote and hope I get something scandalous. I hire a bot-net from some really shady dudes who control 1000 compromised machines in the UK just for election day. I capture the voting habits of 1000 voters on election day. I notice 5 of them have voted BNP. I look these users up and check out their machines, I look through their documents on their machine and find out their names and addresses. I find out one of them is the wife of a tory MP. I leak 'wife of tory mp is a fascist!' to some blogger I know. It hits the internet and goes viral, swings an election. That's a serious problem! So, what are the best techniques for running software where user interactions with the software must be kept secret, on a machine which is possibly compromised?

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• Does a garbage collector collect stack memory, heap memory, or both?

  - by kalpesh

  I read lot of articles about garbage collection and almost all article tells about heap memory. so my question is "garbage collection collects stack memory or heap memory or both". thanks Kalpesh

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• Code Golf: Triforce

  - by chpwn

  This is inspired by/taken from this thread: http://www.allegro.cc/forums/thread/603383 The Problem Assume the user gives you a numeric input ranging from 1 to 7. Input should be taken from the console, arguments are less desirable. When the input is 1, print the following: *********** ********* ******* ***** *** * Values greater than one should generate multiples of the pattern, ending with the one above, but stacked symmetrically. For example, 3 should print the following: *********** *********** *********** ********* ********* ********* ******* ******* ******* ***** ***** ***** *** *** *** * * * *********** *********** ********* ********* ******* ******* ***** ***** *** *** * * *********** ********* ******* ***** *** * Bonus points if you print the reverse as well. *********** *********** ********* ********* ******* ******* ***** ***** *** *** * * *********** ********* ******* ***** *** * * *** ***** ******* ********* *********** * * *** *** ***** ***** ******* ******* ********* ********* *********** *********** Can we try and keep it to one answer per language, that we all improve on?

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• How much abstraction is too much?

  - by Daniel Bingham

  In an Object Oriented Program: How much abstraction is too much? How much is just right? I have always been a nuts and bolts kind of guy. I understood the concept behind high levels of encapsulation and abstraction, but always felt instinctively that adding too much would just confuse the program. I always tried to shoot for an amount of abstraction that left no empty classes or layers. And where in doubt, instead of adding a new layer to the hierarchy, I would try and fit something into the existing layers. However, recently I've been encountering more highly abstracted systems. Systems where everything that could require a representation later in the hierarchy gets one up front. This leads to a lot of empty layers, which at first seems like bad design. However, on second thought I've come to realize that leaving those empty layers gives you more places to hook into in the future with out much refactoring. It leaves you greater ability to add new functionality on top of the old with out doing nearly as much work to adjust the old. The two risks of this seem to be that you could get the layers you need wrong. In this case one would wind up still needing to do substantial refactoring to extend the code and would still have a ton of never used layers. But depending on how much time you spend coming up with the initial abstractions, the chance of screwing it up, and the time that could be saved later if you get it right - it may still be worth it to try. The other risk I can think of is the risk of over doing it and never needing all the extra layers. But is that really so bad? Are extra class layers really so expensive that it is much of a loss if they are never used? The biggest expense and loss here would be time that is lost up front coming up with the layers. But much of that time still might be saved later when one can work with the abstracted code rather than more low level code. So when is it too much? At what point do the empty layers and extra "might need" abstractions become overkill? How little is too little? Where's the sweet spot? Are there any dependable rules of thumb you've found in the course of your career that help you judge the amount of abstraction needed?

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• Is there an algorithm for converting quaternion rotations to Euler angle rotations?

  - by Will Baker

  Is there an existing algorithm for converting a quaternion representation of a rotation to an Euler angle representation? The rotation order for the Euler representation is known and can be any of the six permutations (i.e. xyz, xzy, yxz, yzx, zxy, zyx). I've seen algorithms for a fixed rotation order (usually the NASA heading, bank, roll convention) but not for arbitrary rotation order. Furthermore, because there are multiple Euler angle representations of a single orientation, this result is going to be ambiguous. This is acceptable (because the orientation is still valid, it just may not be the one the user is expecting to see), however it would be even better if there was an algorithm which took rotation limits (i.e. the number of degrees of freedom and the limits on each degree of freedom) into account and yielded the 'most sensible' Euler representation given those constraints. I have a feeling this problem (or something similar) may exist in the IK or rigid body dynamics domains. Solved: I just realised that it might not be clear that I solved this problem by following Ken Shoemake's algorithms from Graphics Gems. I did answer my own question at the time, but it occurs to me it may not be clear that I did so. See the answer, below, for more detail. Just to clarify - I know how to convert from a quaternion to the so-called 'Tait-Bryan' representation - what I was calling the 'NASA' convention. This is a rotation order (assuming the convention that the 'Z' axis is up) of zxy. I need an algorithm for all rotation orders. Possibly the solution, then, is to take the zxy order conversion and derive from it five other conversions for the other rotation orders. I guess I was hoping there was a more 'overarching' solution. In any case, I am surprised that I haven't been able to find existing solutions out there. In addition, and this perhaps should be a separate question altogether, any conversion (assuming a known rotation order, of course) is going to select one Euler representation, but there are in fact many. For example, given a rotation order of yxz, the two representations (0,0,180) and (180,180,0) are equivalent (and would yield the same quaternion). Is there a way to constrain the solution using limits on the degrees of freedom? Like you do in IK and rigid body dynamics? i.e. in the example above if there were only one degree of freedom about the Z axis then the second representation can be disregarded. I have tracked down one paper which could be an algorithm in this pdf but I must confess I find the logic and math a little hard to follow. Surely there are other solutions out there? Is arbitrary rotation order really so rare? Surely every major 3D package that allows skeletal animation together with quaternion interpolation (i.e. Maya, Max, Blender, etc) must have solved exactly this problem?

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• How to begin with augmented reality?

  - by Terri

  I'm currently an undergrad in computer science and I'll be entering my final year next year. Augmented reality is something I find to be a really interesting topic, but I have no idea where to start learning about it. Where do you start learning about this topic and what libraries are available?

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• Algorithm for converting hierarchical flat data (w/ ParentID) into sorted flat list w/ indentation l

  - by eagle

  I have the following structure: MyClass { guid ID guid ParentID string Name } I'd like to create an array which contains the elements in the order they should be displayed in a hierarchy (e.g. according to their "left" values), as well as a hash which maps the guid to the indentation level. For example: ID Name ParentID ------------------------ 1 Cats 2 2 Animal NULL 3 Tiger 1 4 Book NULL 5 Airplane NULL This would essentially produce the following objects: // Array is an array of all the elements sorted by the way you would see them in a fully expanded tree Array[0] = "Airplane" Array[1] = "Animal" Array[2] = "Cats" Array[3] = "Tiger" Array[4] = "Book" // IndentationLevel is a hash of GUIDs to IndentationLevels. IndentationLevel["1"] = 1 IndentationLevel["2"] = 0 IndentationLevel["3"] = 2 IndentationLevel["4"] = 0 IndentationLevel["5"] = 0 For clarity, this is what the hierarchy looks like: Airplane Animal Cats Tiger Book I'd like to iterate through the items the least amount of times possible. I also don't want to create a hierarchical data structure. I'd prefer to use arrays, hashes, stacks, or queues. The two objectives are: Store a hash of the ID to the indentation level. Sort the list that holds all the objects according to their left values. When I get the list of elements, they are in no particular order. Siblings should be ordered by their Name property. Update: This may seem like I haven't tried coming up with a solution myself and simply want others to do the work for me. However, I have tried coming up with three different solutions, and I've gotten stuck on each. One reason might be that I've tried to avoid recursion (maybe wrongly so). I'm not posting the partial solutions I have so far since they are incorrect and may badly influence the solutions of others.

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• Which programming languages aren't considered high-level?

  - by hilo

  In informatics theory I hear and read about high-level and low-level languages all time. Yet I don't understand why this is still relevant as there aren't any (relevant) low-level languages except assembler in use today. So you get: Low-level Assembler Definitely not low-level C BASIC FORTRAN COBOL ... High-level C++ Ruby Python PHP ... And if assembler is low-level, how could you put for example C into the same list. I mean: C is extremely high-level compared to assembler. Same even for COBOL, Fortran, etc. So why does everybody keep mentioning high and low-level languages if assembler is really the only low-level language.

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• What is an integer overflow error?

  - by David

  What is an integer overflow error? why do i care about it? how can it be avoided?

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• Rewriting UNIX cal(1)

  - by dharmatech

  Hello, Today I was testing out SRFI 19 and wrote a simple version of the UNIX cal(1) command. Here's a version in R6RS Scheme which runs in Ikarus and Ypsilon. A few example runs. Schemers: How would you write it? Use your favorite implementation. Ruby and Python: I'm guessing that y'all have elegant date and time libraries. I'm sure you can put the Schemers to shame. ;-) Let's see what ya got. I'd also like to see Haskell and golfed versions. Is there a Stack Overflow tag for re-implementations of UNIX commands? :-) Ed

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• Taking "do the simplest thing that could possible work" too far in TDD: testing for a file-name kno

  - by Support - multilanguage SO

  For TDD you have to Create a test that fail Do the simplest thing that could possible work to pass the test Add more variants of the test and repeat Refactor when a pattern emerge With this approach you're supposing to cover all the cases ( that comes to my mind at least) but I'm wonder if am I being too strict here and if it is possible to "think ahead" some scenarios instead of simple discover them. For instance, I'm processing a file and if it doesn't conform to a certain format I am to throw an InvalidFormatException So my first test was: @Test void testFormat(){ // empty doesn't do anything nor throw anything processor.validate("empty.txt"); try { processor.validate("invalid.txt"); assert false: "Should have thrown InvalidFormatException"; } catch( InvalidFormatException ife ) { assert "Invalid format".equals( ife.getMessage() ); } } I run it and it fails because it doesn't throw an exception. So the next thing that comes to my mind is: "Do the simplest thing that could possible work", so I : public void validate( String fileName ) throws InvalidFormatException { if(fileName.equals("invalid.txt") { throw new InvalidFormatException("Invalid format"); } } Doh!! ( although the real code is a bit more complicated, I found my self doing something like this several times ) I know that I have to eventually add another file name and other test that would make this approach impractical and that would force me to refactor to something that makes sense ( which if I understood correctly is the point of TDD, to discover the patterns the usage unveils ) but: Q: am I taking too literal the "Do the simplest thing..." stuff?

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• Skip List vs. Binary Tree

  - by Claudiu

  I recently came across the data structure known as a Skip list. They seem to have very similar behavior to a binary search tree... my question is - why would you ever want to use a skip list over a binary search tree?

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• Raytracing (LoS) on 3D hex-like tile maps

  - by herenvardo

  Greetings, I'm working on a game project that uses a 3D variant of hexagonal tile maps. Tiles are actually cubes, not hexes, but are laid out just like hexes (because a square can be turned to a cube to extrapolate from 2D to 3D, but there is no 3D version of a hex). Rather than a verbose description, here goes an example of a 4x4x4 map: (I have highlighted an arbitrary tile (green) and its adjacent tiles (yellow) to help describe how the whole thing is supposed to work; but the adjacency functions are not the issue, that's already solved.) I have a struct type to represent tiles, and maps are represented as a 3D array of tiles (wrapped in a Map class to add some utility methods, but that's not very relevant). Each tile is supposed to represent a perfectly cubic space, and they are all exactly the same size. Also, the offset between adjacent "rows" is exactly half the size of a tile. That's enough context; my question is: Given the coordinates of two points A and B, how can I generate a list of the tiles (or, rather, their coordinates) that a straight line between A and B would cross? That would later be used for a variety of purposes, such as determining Line-of-sight, charge path legality, and so on. BTW, this may be useful: my maps use the (0,0,0) as a reference position. The 'jagging' of the map can be defined as offsetting each tile ((y+z) mod 2) * tileSize/2.0 to the right from the position it'd have on a "sane" cartesian system. For the non-jagged rows, that yields 0; for rows where (y+z) mod 2 is 1, it yields 0.5 tiles. I'm working on C#4 targeting the .Net Framework 4.0; but I don't really need specific code, just the algorithm to solve the weird geometric/mathematical problem. I have been trying for several days to solve this at no avail; and trying to draw the whole thing on paper to "visualize" it didn't help either :( . Thanks in advance for any answer

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• Data validation best practices: how can I better construct user feedback?

  - by Cory Larson

  Data validation, whether it be domain object, form, or any other type of input validation, could theoretically be part of any development effort, no matter its size or complexity. I sometimes find myself writing informational or error messages that might seem harsh or demanding to unsuspecting users, and frankly I feel like there must be a better way to describe the validation problem to the user. I know that this topic is subjective and argumentative. StackOverflow might not be the proper channel for diving into this subject, but like I've mentioned, we all run into this at some point or another. There are so many StackExchange sites now; if there is a better one, feel free to share! Basically, I'm looking for good resources on data validation and user feedback that results from it at a theoretical level. Topics and questions I'm interested in are: Content Should I be describing what the user did correctly or incorrectly, or simply what was expected? How much detail can the user read before they get annoyed? (e.g. Is "Username cannot exceed 20 characters." enough, or should it be described more fully, such as "The username cannot be empty, and must be at least 6 characters but cannot exceed 30 characters."?) Grammar How do I decide between phrases like "must not," "may not," or "cannot"? Delivery This can depend on the project, but how should the information be delivered to the user? Should it be obtrusive (e.g. JavaScript alerts) or friendly? Should they be displayed prominently? Immediately (i.e. without confirmation steps, etc.)? Logging Do you bother logging validation errors? Internationalization Some cultures prefer or better understand directness over subtlety and vice-versa (e.g. "Don't do that!" vs. "Please check what you've done."). How do I cater to the majority of users? I may edit this list as I think more about the topic, but I'm genuinely interest in proper user feedback techniques. I'm looking for things like research results, poll results, etc. I've developed and refined my own techniques over the years that users seem to be okay with, but I work in an environment where the users prefer to adapt to what you give them over speaking up about things they don't like. I'm interested in hearing your experiences in addition to any resources to which you may be able to point me.

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• Real world use cases of bitwise operators

  - by Olivier Lalonde

  What are some real world use cases of the following bitwise operators? AND XOR NOT OR

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• Code Golf - Banner Generation

  - by Claudiu

  When thanking someone, you don't want to just send them an e-mail saying "Thanks!", you want to have something FLASHY: Input: THANKS!! Output: TTT H H AAA N N K K SSS !!! !!! T H H A A NNN K K S !!! !!! T HHH AAA NNN KK SSS !!! !!! T H H A A N N K K S T H H A A N N K K SSS !!! !!! Write a program to generate a banner. You only have to generate upper-case A-Z along with spaces and exclamation points (what is a banner without an exclamation point?). All characters are made up of a 3x5 grid of the same character (so the S is a 3x5 grid made of S). All output should be on one row (so no newlines). Here are all the letters you need: Input: ABCDEFGHIJKL Output: AAA BBB CCC DD EEE FFF GGG H H III JJJ K K L A A B B C D D E F G H H I J K K L AAA BBB C D D EE FF G G HHH I J KK L A A B B C D D E F G G H H I J J K K L A A BBB CCC DD EEE F GGG H H III JJJ K K LLL Input: MNOPQRSTUVWX Output: M M N N OOO PPP QQQ RR SSS TTT U U V V W W X X MMM NNN O O P P Q Q R R S T U U V V W W X M M NNN O O PPP Q Q RR SSS T U U V V WWW X M M N N O O P QQQ R R S T U U V V WWW X M M N N OOO P QQQ R R SSS T UUU V WWW X X Input: YZ! Output: Y Y ZZZ !!! Y Y Z !!! YYY Z !!! Y Z YYY ZZZ !!! The winner is the shortest source code. Source code should read input from stdin, output to stdout. You can assume input will only contain [A-Z! ]. If you insult the user on incorrect input, you get a 10 character discount =P. I was going to require these exact 27 characters, but to make it more interesting, you can choose how you want them to look - whatever makes your code shorter! To prove that your letters do look like normal letters, show the output of the last three runs.

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• method for specialized pathfinding?

  - by rlbond

  I am working on a roguelike in my (very little) free time. Each level will basically be a few rectangular rooms connected together by paths. I want the paths between rooms to be natural-looking and windy, however. For example, I would not consider the following natural-looking: B X X X XX XX XX AXX I really want something more like this: B X XXXX X X X X AXXXXXXXX These paths must satisfy a few properties: I must be able to specify an area inside which they are bounded, I must be able to parameterize how windy and lengthy they are, The lines should not look like they started at one path and ended at the other. For example, the first example above looks as if it started at A and ended at B, because it basically changed directions repeatedly until it lined up with B and then just went straight there. I was hoping to use A*, but honestly I have no idea what my heuristic would be. I have also considered using a genetic algorithm, but I don't know how practical that method might end up. My question is, what is a good way to get the results I want? Please do not just specify a method like "A*" or "Dijkstra's algorithm," because I also need help with a good heuristic.

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• How to show validation messages in MVC?

  - by Ian Boyd

  When a user tries to click:        Save and they have entered in some invalid data, i want to notify them. This can be with methods such as: directing their attention to the thing that needs their attention with a balloon hint automatically dropping down a combo-box triggering an animation showing a modal dialog box etc What is the mechanism where a controller tells the view to show a validation message for some controls, given that different views have different notification methods? p.s. the controller doesn't know the order that controls are physically arranged in the view (e.g. LTR locale wants to notify the user in a top-down-left-to-right visual order, while RTL locale wants to notify the user in a bottom-up-right-to-left order)

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• Low latency programming

  - by Sambatyon

  I've been reading a lot about low latency financial systems (especially since the famous case of corporate espionage) and the idea of low latency systems has been in my mind ever since. There are a million applications that can use what these guys are doing, so I would like to learn more about the topic. The thing is I cannot find anything valuable about the topic. Can anybody recommend books, sites, examples on low latency systems?

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• In what programing language are the things i actualy care about writin? [closed]

  - by David

  To be more specific and less subjective: In what language are video games like Halo 3/COD 4/ mario cart written? Microsoft word for windows? for mac? The animation software used by big movie studios to make movies like toystory and monsters inc? The software that helps pilots control the F22 raptor? The software that watches the stock market? The software in the computer in my car? The software that makes the internet work? (this one is a bit vague, if more specificness is needed then google specifically) robots?

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• Code Golf: Word Search Solver

  - by Maxim Z.

  Note: This is my first Code Golf challenge/question, so I might not be using the correct format below. I'm not really sure how to tag this particular question, and should this be community wiki? Thanks! This Code Golf challenge is about solving word searches! A word search, as defined by Wikipedia, is: A word search, word find, word seek, word sleuth or mystery word puzzle is a word game that is letters of a word in a grid, that usually has a rectangular or square shape. The objective of this puzzle is to find and mark all the words hidden inside the box. The words may be horizontally, vertically or diagonally. Often a list of the hidden words is provided, but more challenging puzzles may let the player figure them out. Many word search puzzles have a theme to which all the hidden words are related. The word searches for this challenge will all be rectangular grids with a list of words to find provided. The words can be written vertically, horizontally, or diagonally. Input/Output The user inputs their word search and then inputs a word to be found in their grid. These two inputs are passed to the function that you will be writing. It is up to you how you want to declare and handle these objects. Using a strategy described below or one of your own, the function finds the specific word in the search and outputs its starting coordinates (simply row number and column number) and ending coordinates. If you find two occurrences of the word, you must output both's set of coordinates. Example Input: A I Y R J J Y T A S V Q T Z E X B X G R Z P W V T B K U F O E A F L V F J J I A G B A J K R E S U R E P U S C Y R S Y K F B B Q Y T K O I K H E W G N G L W Z F R F H L O R W A R E J A O S F U E H Q V L O A Z B J F B G I F Q X E E A L W A C F W K Z E U U R Z R T N P L D F L M P H D F W H F E C G W Z B J S V O A O Y D L M S T C R B E S J U V T C S O O X P F F R J T L C V W R N W L Q U F I B L T O O S Q V K R O W G N D B C D E J Y E L W X J D F X M Word to find: codegolf Output: row 12, column 8 --> row 5, column 1 Strategies Here are a few strategies you might consider using. It is completely up to you to decide what strategy you want to use; it doesn't have to be in this list. Looking for the first letter of the word; on each occurrence, looking at the eight surrounding letters to see whether the next letter of the word is there. Same as above, except looking for a part of a word that has two of the same letter side-by-side. Counting how often each letter of the alphabet is present in the whole grid, then selecting one of the least-occurring letters from the word you have to find and searching for the letter. On each occurrence of the letter, you look at its eight surrounding letters to see whether the next and previous letters of the word is there.

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• What problems have you solved using genetic algorithms/genetic programming?

  - by knorv

  Genetic algorithms (GA) and genetic programming (GP) are interesting areas of research. I'd like to know about specific problems you - the SO reader - have solved using GA/GP and what libraries/frameworks you used if you didn't roll your own. Questions: What problems have you used GA/GP to solve? What libraries/frameworks did you use? I'm looking for first-hand experiences, so please do not answer unless you have that.

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• 3 dimensional bin packing algorithms

  - by BuschnicK

  I'm faced with a 3 dimensional bin packing problem and am currently conducting some preliminary research as to which algorithms/heuristics are currently yielding the best results. Since the problem is NP hard I do not expect to find the optimal solution in every case, but I was wondering: 1) what are the best exact solvers? Branch and Bound? What problem instance sizes can I expect to solve with reasonable computing resources? 2) what are the best heuristic solvers? 3) What off-the-shelf solutions exist to conduct some experiments with?

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• Bitwise Interval Arithmetic

  - by KennyTM

  I've recently read an interesting thread on the D newsgroup, which basically asks, Given two signed integers a ∈ [amin, amax], b ∈ [bmin, bmax], what is the tightest interval of a | b? I'm think if interval arithmetics can be applied on general bitwise operators (assuming infinite bits). The bitwise-NOT and shifts are trivial since they just corresponds to -1 − x and 2n x. But bitwise-AND/OR are a lot trickier, due to the mix of bitwise and arithmetic properties. Is there a polynomial-time algorithm to compute the intervals of bitwise-AND/OR? Note: Assume all bitwise operations run in linear time (of number of bits), and test/set a bit is constant time. The brute-force algorithm runs in exponential time. Because ~(a | b) = ~a & ~b and a ^ b = (a | b) & ~(a & b), solving the bitwise-AND and -NOT problem implies bitwise-OR and -XOR are done. Although the content of that thread suggests min{a | b} = max(amin, bmin), it is not the tightest bound. Just consider [2, 3] | [8, 9] = [10, 11].)

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