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  • How to teach computer science ?

    - by proferikson
    I am just starting to teach computer science. It's just the basic level. I'm finding that I sometimes don't know how to approach topics in a way that lets students easily understand. I've found that the best thing is to use analogies. A terrible one, that worked well, was presenting recursion by using the process of eating a burger. (You eat one bite, then you eat the rest). Interesting real world examples do wonders here. I'd like to know the techniques you have used for teaching, or teachers you've had have used that proved particularly effective. I'd also like to know your best analogies and examples for topics in CS101, especially for those harder to grasp topics. I'm teaching the class in Java (as required).

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  • How important do you find exception safety to be in your C++ code?

    - by Kai
    Every time I consider making my code strongly exception safe, I justify not doing it because it would be so time consuming. Consider this relatively simple snippet: Level::Entity* entity = new Level::Entity(); entity->id = GetNextId(); entity->AddComponent(new Component::Position(x, y)); entity->AddComponent(new Component::Movement()); entity->AddComponent(new Component::Render()); allEntities.push_back(entity); // std::vector entityById[entity->id] = entity; // std::map return entity; To implement a basic exception guarantee, I could use a scoped pointer on the new calls. This would prevent memory leaks if any of the calls were to throw an exception. However, let's say I want to implement a strong exception guarantee. At the least, I would need to implement a shared pointer for my containers (I'm not using Boost), a nothrow Entity::Swap for adding the components atomically, and some sort of idiom for atomically adding to both the Vector and Map. Not only would these be time consuming to implement, but they would be expensive since it involves a lot more copying than the exception unsafe solution. Ultimately, it feels to me like that time spent doing all of that wouldn't be justified just so that the a simple CreateEntity function is strongly exception safe. I probably just want the game to display an error and close at that point anyway. How far do you take this in your own game projects? Is it generally acceptable to write exception unsafe code for a program that can just crash when there is an exception?

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  • Best exception handling practices or recommendations?

    - by user828584
    I think the two main problems with my programs are my code structure/organization and my error handling. I'm reading Code Complete 2, but I need something to read for working with potential problems. For example, on a website, if something can only happen if the user tampers with data via javascript, do you write for that? Also, when do you not catch errors? When you write a class that expects a string and an int as input, and they aren't a string and int, do you check for that, or do you let it bubble up to the calling method that passed incorrect parameters? I know this is a broad topic that can't be answered in a single answer here, so what I'm looking for is a book or resource that's commonly accepted as teaching proper exception handling practice.

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  • Beat detection and FFT

    - by Quincy
    So I am working on a platformer game which includes music with beat detection. I am currently using a simple if the energy that is stored in the history buffer is smaller then the current energy there is a beat. The problem with this is that ofcourse if you use songs like rock songs where you have a pretty steady amplitude this isn't going to work. So I looked further and found algorithms splitting the sound into multiple bands using FFT. I then found this : http://en.literateprograms.org/Cooley-Tukey_FFT_algorithm_(C) The only problem I'm having is that I am quite new to audio and I have no idea how to use that to split the signal up into multiple signals. So my question is : How do you use a FFT to split a signal into multiple bands ? Also for the guys interested, this is my algorithm in c# : // C = threshold, N = size of history buffer / 1024 public void PlaceBeatMarkers(float C, int N) { List<float> instantEnergyList = new List<float>(); short[] samples = soundData.Samples; float timePerSample = 1 / (float)soundData.SampleRate; int sampleIndex = 0; int nextSamples = 1024; // Calculate instant energy for every 1024 samples. while (sampleIndex + nextSamples < samples.Length) { float instantEnergy = 0; for (int i = 0; i < nextSamples; i++) { instantEnergy += Math.Abs((float)samples[sampleIndex + i]); } instantEnergy /= nextSamples; instantEnergyList.Add(instantEnergy); if(sampleIndex + nextSamples >= samples.Length) nextSamples = samples.Length - sampleIndex - 1; sampleIndex += nextSamples; } int index = N; int numInBuffer = index; float historyBuffer = 0; //Fill the history buffer with n * instant energy for (int i = 0; i < index; i++) { historyBuffer += instantEnergyList[i]; } // If instantEnergy / samples in buffer < instantEnergy for the next sample then add beatmarker. while (index + 1 < instantEnergyList.Count) { if(instantEnergyList[index + 1] > (historyBuffer / numInBuffer) * C) beatMarkers.Add((index + 1) * 1024 * timePerSample); historyBuffer -= instantEnergyList[index - numInBuffer]; historyBuffer += instantEnergyList[index + 1]; index++; } }

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  • How can I compare between web development technologies?

    - by Steve
    I would like experts to explain for me how can I compare between web development tools or technologies in order to be able to choose the right one. I'm tired from searching always in the regular way: X Technology vs Y Technology. I'm tired from peoples' biased opinions and usually I don't find a fair comparison. I have decided to put my question here about how can I compare them so you may identify to me the main standards for comparisons so I can compare them by myself and becoming able to choose the technology that is appropriate for the project I will develop. Note: in web development technologies I mean server side languages (e.g. PHP). One important requirement for me that can be defined as major one is cost efficiency and I mean that I don't care about the cost in the near future or the current cost, but what is more important for me is the cost in the future. If, for example, the site becomes one of the most 100 visited sites.   So, how can I compare the cost of different technologies for a future status of a site (such as being very famous site) so I can scale my option easily without missing a good technology like what happened with some sites when they chose not the most effective tool.

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  • How to recover from finite-state-machine breakdown?

    - by Earl Grey
    My question may seems very scientific but I think it's a common problem and seasoned developers and programmers hopefully will have some advice to avoid the problem I mention in title. Btw., what I describe bellow is a real problem I am trying to proactively solve in my iOS project, I want to avoid it at all cost. By finite state machine I mean this I have a UI with a few buttons, several session states relevant to that UI and what this UI represents, I have some data which values are partly displayed in the UI, I receive and handle some external triggers (represented by callbacks from sensors). I made state diagrams to better map the relevant scenarios that are desirable and alowable in that UI and application. As I slowly implement the code, the app starts to behave more and more like it should. However, I am not very confident that it is robust enough. My doubts come from watching my own thinking and implementation process as it goes. I was confident that I had everything covered, but it was enough to make a few brute tests in the UI and I quickly realized that there are still gaps in the behavior ..I patched them. However, as each component depends and behaves based on input from some other component, a certain input from user or some external source trigers a chain of events, state changes..etc. I have several components and each behave like this Trigger received on input - trigger and its sender analyzed - output something (a message, a state change) based on analysis The problem is, this is not completely selfcontained, and my components (a database item, a session state, some button's state)...COULD be changed, influenced, deleted, or otherwise modified, outside the scope of the event-chain or desirable scenario. (phone crashes, battery is empty phone turn of suddenly) This will introduce a nonvalid situation into the system, from which the system potentially COULD NOT BE ABLE to recover. I see this (althought people do not realize this is the problem) in many of my competitors apps that are on apple store, customers write things like this "I added three documents, and after going there and there, i cannot open them, even if a see them." or "I recorded videos everyday, but after recording a too log video, I cannot turn of captions on them.., and the button for captions doesn't work".. These are just shortened examples, customers often describe it in more detail..from the descriptions and behavior described in them, I assume that the particular app has a FSM breakdown. So the ultimate question is how can I avoid this, and how to protect the system from blocking itself? EDIT I am talking in the context of one viewcontroller's view on the phone, I mean one part of the application. I Understand the MVC pattern, I have separate modules for distinct functionality..everything I describe is relevant to one canvas on the UI.

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  • Writing use cases for XML mapping scenarios between two different systems

    - by deepak_prn
    I am having some trouble writing use cases for XML mapping after a certain trigger invoked by the system. For example, one of the scenarios goes: the store cashier sells an item, the transaction data is sent to Data management system. Now, I am writing a functional design for the scenario which deals with mapping XML fields between our system and the data management system. Question : I was wondering if some one had to deal with writing use cases or extension use cases for mapping XML fields between two systems? (There is no XSLT involved) and if you used a table to represent the fields mapping (example is below) or any other visualization tool which does not break the bank ? I searched many questions on SO and here but nothing came close to my requirement.

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  • how to programtically build a grid of interlocking but random sized squares

    - by Mrwolfy
    I want to create a two dimensional layout of rectangular shapes, a grid made up of random sized cubes. The cubed should fit together and have equal padding or margin (space between). Kind of like a comic book layout, or more like the image attached. How could I do this procedurally? Practically, I would probably be using Python and some graphic software to render an image, but I don't know the type of algorithm (or whatnot) I would need to use to generate the randomized grid.

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  • deciphering columnar transposition cipher

    - by Arfan M
    I am looking for an idea on how to decipher a columnar transposition cipher without knowing the key or the length of the key. When I take the cipher text as input to my algorithm I will guess the length of the key to be the factors of the length of the cipher text. I will take the first factor suppose the length was 20 letters so I will take 2*10 (2 rows and 10 columns). Now I want to arrange the cipher text in the columns and read it row wise to see if there is any word forming and match it with a dictionary if it is something sensible. If it matches the dictionary then it means it is in correct order or else I want to know how to make other combinations of the columns and read the string again row wise. Please suggest another approach that is more efficient.

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  • Making game constants/tables available to game logic classes/routines in a modular manner

    - by Extrakun
    Suppose I have a game where there are several predefined constants and charts (a XP chart, cost of goods and so on). Those could be defined at runtime, or load from files at start-up. The question is how should those logic routines access the constants and charts? For example, I could try using global variables, but that cause all classes relying on the variables to be tightly coupled with them.

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  • Get entities ids from two similar collections using one method

    - by Patryk Roszczyniala
    I've got two lists: List<Integer, ZooEntity> zoos; List<Integer, List<ZooEntity>> groupOfZoos; These operations will return collections of values: Collection<ZooEntity> cz = zoos.values(); Collection<List<ZooEntity>> czList = groupOfZoos.values(); What I want to achieve is to get list of all zoo ids. List<Integer> zooIds = cz ids + czList ids; Of course I can create two methods to do what I want: public List<Integer> getIdsFromFlatList(Collection<ZooEntity> list) { List<Integer> ids = new ArrayList<Integer>(); for (ZooEntity z : list) { ids.add(z.getId()); } return ids; } public List<Integer> getIdsFromNestedList(Collection<List<ZooEntity>> list) { List<Integer> ids = new ArrayList<Integer>(); for (List<ZooEntity> zList : list) { for (ZooEntity z : zList) { ids.add(z.getId()); } } return ids; } As you can see those two methods are very similar and here is my question: Is it good to create one method (for example using generics) which will get ids from those two lists (zoos and groupOfZoos). If yes how it should look like? If no what is the best solution? BTW. This is only the example. I've got very similar problem at job and I want to do it in preety way (I can't change enities, I can change only getIds...() methods).

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  • How do functional languages handle random numbers?

    - by Electric Coffee
    What I mean about that is that in nearly every tutorial I've read about functional languages, is that one of the great things about functions, is that if you call a function with the same parameters twice, you'll always end up with the same result. How on earth do you then make a function that takes a seed as a parameter, and then returns a random number based on that seed? I mean this would seem to go against one of the things that are so good about functions, right? Or am I completely missing something here?

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  • Collision Resolution

    - by ultifinitus
    Hey all, I'm making a simple side-scrolling game, and I would appreciate some input! My collision detection system is a simple bounding box detection, so it's really easy to implement. However my collision resolution is ridiculous! Currently I have a little formula like this: if (colliding(firstObject,secondObject)) firstObject.resolve_collision(yAxisOffset); if (colliding(firstObject,secondObject)) firstObject.resolve_collision(xAxisOffset); where yAxisOffset is only set if the first object's previous y position was outside the second object's collision frame, respectively xAxisOffset as well. Now this is working great, in general. However there is a single problem. When I have a stack of objects and I push the first object against that stack, the first object get's "stuck," on the stack. What's I think is happening is the object's collision system checks and resolves for collisions based on creation time, so If I check one axis, then the other, the object will "sink" object directly along the checking axis. This sinking action causes the collision detection routine to think there's a gap between our position and the other object's position, and when I finally check the object that I've already sunk into, my object's position is resolved to it's original position... All this is great, and I'm sure if I bang my head against a wall long enough i'll come up with a working algorithm, but I'd rather not =). So what in the heck do you think I should do? How could I change my collision resolution system to fix this? Here's the program (temporary link, not sure how long it'll last) (notes: arrow keys to navigate, click to drop block, x to jump) I'd appreciate any help you can offer!

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  • Finding Stuff in SQL Server Database DDL

    You'd have thought that nothing would be easier than using SQL Server Management Studio (SSMS) for searching through the DDL for both the names and definitions of the structural metadata of your databases, for the occurrence of a particular string of letters. Not so easy, it turns out, though Phil Factor is able to come up with various methods for various purposes.

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  • Should main method be only consists of object creations and method calls?

    - by crucified soul
    A friend of mine told me that, the best practice is class containing main method should be named Main and only contains main method. Also main method should only parse inputs, create other objects and call other methods. The Main class and main method shouldn't do anything else. Basically what he is saying that class containing main method should be like: public class Main { public static void main(String[] args) { //parse inputs //create other objects //call methods } } Is it the best practice?

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  • Modifying Contiguous Time Periods in a History Table

    Alex Kuznetsov is credited with a clever technique for creating a history table for SQL that is designed to store contiguous time periods and check that these time periods really are contiguous, using nothing but constraints. This is now increasingly useful with the DATE data type in SQL Server. The modification of data in this type of table isn't always entirely intuitive so Alex is on hand to give a brief explanation of how to do it.

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  • Build one to throw away vs Second-system effect

    - by m3th0dman
    One one hand there is an advice that says "Build one to throw away". Only after finishing a software system and seeing the end product we realize what went wrong in the design phase and understand how we should have really done it. On the other hand there is the "second-system effect" which says that the second system of the same kind that is designed is usually worse than the first one; there are many features that did not fit in the first project and were pushed into the second version usually leading to overly complex and overly engineered. Isn't here some contradiction between these principles? What is the correct view over the problems and where is the border between these two? I believe that these "good practices" are were firstly promoted in the seminal book The Mythical Man-Month by Fred Brooks. I know that some of these issues are solved by Agile methodologies, but deep down, the problem is still the principles still stand; for example we would not make important design changes 3 sprints before going live.

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  • Low coupling and tight cohesion

    - by hidayat
    Of course it depends on the situation. But when a lower lever object or system communicate with an higher level system, should callbacks or events be preferred to keeping a pointer to higher level object? For example, we have a world class that has a member variable vector<monster> monsters. When the monster class is going to communicate with the world class, should I prefer using a callback function then or should I have a pointer to the world class inside the monster class?

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  • How to begin in Game Development? [closed]

    - by Bladimir Ruiz
    It's been a while since I decide to get into game dev, but, there are so many ways to make a game, that i dont know where to begin, I got unity 3d license for PC/Android/Ios for free, but i Also got XNA dev tool, ALSO have CoronaSDK.. But I dont Know wich one to use. Till' now all i want is to make a Sidecroller lime Super Mario Bros, Just for start later on, i will like to make diferent games. In the future i would like to work in the game industry which tools will be the best to Start in that "Dream"?

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  • Can somebody guide me asto how I can make a game for playing cards [closed]

    - by user2558
    In college me and my friends use to play cards all the time. I want to make a game for that. It's quite similar to hearts, a kind of modified hearts which we made up. I want to make a multiplayer game which could be played over the internet. Plus there should also be an option for computer to play if less players availiable at the time. I don't want to make a exe. I want to play in browser. How should I go about it.

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  • Getting rid of getting stuck often [closed]

    - by Pankaj Upadhyay
    I have been working with C# and .NET for around 2-3 years. But, still i get stuck too often. My project includes few simple websites(asp.net) in the early parts and then a desktop application for cotton transaction management(wpf). And right now, I am building a price compare website (asp.net MVC). Along the lines, I have read quite few books on C# and .NET, but still I get stuck very often. What pisses me is that the problems I get stuck in aren't very typical or hard. You can get a better idea by visiting my questions page on SO. After looking at my question lists, do you also feel that my basis or knowledge as a programmer are weak ? If so, How can i find a remedy to this problem ? And How can I stop getting stuck too often for simpler problems.

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  • GLSL, is it possible to offsetting vertices based on height map colour?

    - by Rob
    I am attempting to generate some terrain based upon a heightmap. I have generated a 32 x 32 grid and a corresponding height map - In my vertex shader I am trying to offset the position of the Y axis based upon the colour of the heightmap, white vertices being higher than black ones. //Vertex Shader Code #version 330 uniform mat4 modelMatrix; uniform mat4 viewMatrix; uniform mat4 projectionMatrix; uniform sampler2D heightmap; layout (location=0) in vec4 vertexPos; layout (location=1) in vec4 vertexColour; layout (location=3) in vec2 vertexTextureCoord; layout (location=4) in float offset; out vec4 fragCol; out vec4 fragPos; out vec2 fragTex; void main() { // Retreive the current pixel's colour vec4 hmColour = texture(heightmap,vertexTextureCoord); // Offset the y position by the value of current texel's colour value ? vec4 offset = vec4(vertexPos.x , vertexPos.y + hmColour.r, vertexPos.z , 1.0); // Final Position gl_Position = projectionMatrix * viewMatrix * modelMatrix * offset; // Data sent to Fragment Shader. fragCol = vertexColour; fragPos = vertexPos; fragTex = vertexTextureCoord; } However the code I have produced only creates a grid with none of the y vertices higher than any others.

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  • runtime error: invalid memory address or nil pointer dereference

    - by Klink
    I want to learn OpenGL 3.0 with golang. But when i try to compile some code, i get many errors. package main import ( "os" //"errors" "fmt" //gl "github.com/chsc/gogl/gl33" //"github.com/jteeuwen/glfw" "github.com/go-gl/gl" "github.com/go-gl/glfw" "runtime" "time" ) var ( width int = 640 height int = 480 ) var ( points = []float32{0.0, 0.8, -0.8, -0.8, 0.8, -0.8} ) func initScene() { gl.Init() gl.ClearColor(0.0, 0.5, 1.0, 1.0) gl.Enable(gl.CULL_FACE) gl.Viewport(0, 0, 800, 600) } func glfwInitWindowContext() { if err := glfw.Init(); err != nil { fmt.Fprintf(os.Stderr, "glfw_Init: %s\n", err) glfw.Terminate() } glfw.OpenWindowHint(glfw.FsaaSamples, 1) glfw.OpenWindowHint(glfw.WindowNoResize, 1) if err := glfw.OpenWindow(width, height, 0, 0, 0, 0, 32, 0, glfw.Windowed); err != nil { fmt.Fprintf(os.Stderr, "glfw_Window: %s\n", err) glfw.CloseWindow() } glfw.SetSwapInterval(1) glfw.SetWindowTitle("Title") } func drawScene() { for glfw.WindowParam(glfw.Opened) == 1 { gl.Clear(gl.COLOR_BUFFER_BIT) vertexShaderSrc := `#version 120 attribute vec2 coord2d; void main(void) { gl_Position = vec4(coord2d, 0.0, 1.0); }` vertexShader := gl.CreateShader(gl.VERTEX_SHADER) vertexShader.Source(vertexShaderSrc) vertexShader.Compile() fragmentShaderSrc := `#version 120 void main(void) { gl_FragColor[0] = 0.0; gl_FragColor[1] = 0.0; gl_FragColor[2] = 1.0; }` fragmentShader := gl.CreateShader(gl.FRAGMENT_SHADER) fragmentShader.Source(fragmentShaderSrc) fragmentShader.Compile() program := gl.CreateProgram() program.AttachShader(vertexShader) program.AttachShader(fragmentShader) program.Link() attribute_coord2d := program.GetAttribLocation("coord2d") program.Use() //attribute_coord2d.AttribPointer(size, typ, normalized, stride, pointer) attribute_coord2d.EnableArray() attribute_coord2d.AttribPointer(0, 3, false, 0, &(points[0])) //gl.DrawArrays(gl.TRIANGLES, 0, len(points)) gl.DrawArrays(gl.TRIANGLES, 0, 3) glfw.SwapBuffers() inputHandler() time.Sleep(100 * time.Millisecond) } } func inputHandler() { glfw.Enable(glfw.StickyKeys) if glfw.Key(glfw.KeyEsc) == glfw.KeyPress { //gl.DeleteBuffers(2, &uiVBO[0]) glfw.Terminate() } if glfw.Key(glfw.KeyF2) == glfw.KeyPress { glfw.SetWindowTitle("Title2") fmt.Println("Changed to 'Title2'") fmt.Println(len(points)) } if glfw.Key(glfw.KeyF1) == glfw.KeyPress { glfw.SetWindowTitle("Title1") fmt.Println("Changed to 'Title1'") } } func main() { runtime.LockOSThread() glfwInitWindowContext() initScene() drawScene() } And after that: panic: runtime error: invalid memory address or nil pointer dereference [signal 0xb code=0x1 addr=0x0 pc=0x41bc6f74] goroutine 1 [syscall]: github.com/go-gl/gl._Cfunc_glDrawArrays(0x4, 0x7f8500000003) /tmp/go-build463568685/github.com/go-gl/gl/_obj/_cgo_defun.c:610 +0x2f github.com/go-gl/gl.DrawArrays(0x4, 0x3, 0x0, 0x45bd70) /tmp/go-build463568685/github.com/go-gl/gl/_obj/gl.cgo1.go:1922 +0x33 main.drawScene() /home/klink/Dev/Go/gogl/gopher/exper.go:85 +0x1e6 main.main() /home/klink/Dev/Go/gogl/gopher/exper.go:116 +0x27 goroutine 2 [syscall]: created by runtime.main /build/buildd/golang-1/src/pkg/runtime/proc.c:221 exit status 2

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  • Best way to indicate more results available

    - by Alex Stangl
    We have a service to return messages. We want to limit the number returned, either allowing the caller to specify the max number to return, or else to use an internal hard limit. We also have thought it would be nice to include in the response whether more messages are available. The "best" way to go about this is not clear. Here are some ideas so far: Only set the "more messages" indicator if the user did not specify a max limit, and the internal max limit was hit. Same as #1 except that "more messages" indicator set regardless of whether the internal hard limit is hit, or the user-specified limit is hit. Same as #1 (or #2) except that we internally read limit + 1 records, but only return limit records, so we know "for sure" there is at least one additional message rather than "maybe" there are additional messages. Do away with the "more messages" flag, as it is confusing and unnecessary. Instead force the user to keep calling the API until it returns no messages. Change "more messages" indicator to something more akin to an EOF indicator, only set when the last message is known to have been retrieved and returned. What do you think is the best solution? (Doesn't have to be one of the above choices.) I searched and couldn't find a similar question already asked. Hopefully this is not "too subjective".

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  • How to implement a score database in Android

    - by Michael Seun Araromi
    I making a 2d game for android using opengl-es technology. It is a space shooting game where the player shoots enemy ships. I want to keep a track of score for the amount of enemy ships destroyed and a record of a local highscore, I want the score to be incremented whenever an enemy is destroyed. I also want a way of displaying both score and highscore on the game screen. I am not farmiliar with databases at all and I will appreciate a clear answer or a link to a good tutorial for my cause. Thanks

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