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  • Why do I not get the correct answer for Euler 56 in J?

    - by Gregory Higley
    I've solved 84 of the Project Euler problems, mostly in Haskell. I am now going back and trying to solve in J some of those I already solved in Haskell, as an exercise in learning J. Currently, I am trying to solve Problem 56. Let me stress that I already know what the right answer is, since I've already solved it in Haskell. It's a very easy, trivial problem. I will not give the answer here. Here is my solution in J: digits =: ("."0)":"0 eachDigit =: adverb : 'u@:digits"0' NB. I use this so often I made it an adverb. cartesian =: adverb : '((#~ #) u ($~ ([:*~#)))' >./ +/ eachDigit x: ^ cartesian : i. 99 This produces a number less than the desired result. In other words, it's wrong somehow. Any J-ers out there know why? I'm baffled, since it's pretty straightforward and totally brute force.

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  • Beginner question: What is binding?

    - by JDelage
    Hi, I was trying to understand the difference between early and late binding, and in the process realized that the concept of binding is nebulous to me. I think I understand that it relates to the way data-as-a-word-of-memory is linked to type-as-a-set-of-language-features but I am not sure those are the right concepts. Also, how does understanding this deeply help people become better programmers? Please note: This question is not "what is late v. early binding" or "what are the trade-offs between the 2". Those already exist here. Thanks, JDelage

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  • Best second language to learn for a native english speaking programmer?

    - by Tom Dignan
    I have always wanted to learn a foreign language, but I would like to pick one that can also help me the most in my career. I'm in the US, so it is not necessary for me to learn a second language to influence my career success, however I think knowing one and speaking it fluently could potentially put me in a more interesting career than if I did not. I would like to be able to travel the world, especially if I could have a reason to go one place or another. Which leads me to my question: What is the best second language to learn for a native English speaking programmer? (Especially from the US) Some ideas that come to mind for me are Mandarin, German, Japanese, French... I am looking for experienced opinions though! Thanks.

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  • FTP to SFTP in shell scripting

    - by Kimi
    This script is to connect to different servers and copy a file from a loaction defined. It is mandatory to use sftp and not ftp. #!/usr/bin/ksh -xvf Detail="jyotibo|snv4915|/tlmusr1/tlm/rt/jyotibo/JyotiBo/ jyotibo|snv4915|/tlmusr1/tlm/rt/jyotibo/JyotiBo/" password=Unix11! c_filename=import.log localpath1=`pwd` for i in $Detail do echo $i UserName=`echo $i | cut -d'|' -f1` echo $UserName remotehost=`echo $i | cut -d'|' -f2` echo $remotehost remote_path=`echo $i | cut -d'|' -f3` echo $remote_path { echo "open $remotehost user $UserName $password lcd $localpath1 cd $remote_path bi prompt mget $c_filename prompt " } |ftp -i -n -v 2>&1 done I want to do the similar thing using sftp instead of ftp.

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  • Can any genius out there turn this code from generating permutation to generating combination?

    - by mark
    #include <string> int main(int,char**) { std::string default_str = "12345"; int perm=1, digits=default_str.size(); for (int i=1;i<=digits;perm*=i++); for (int a=0;a<perm;a++) { std::string avail=default_str; for (int b=digits,div=perm;b>0; b--) { div/=b; int index = (a/div)%b; printf("%c", avail[index] ); avail.erase(index,1) ; } printf("\n"); } printf("permutations:%d\n",perm); while(1); }

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  • Why Do You Use Delphi?

    - by lkessler
    Nick Bradbury (the author of HomeSite, TopStyle and FeedDemon) just posted a fascinating explanation of why he uses Delphi: http://nick.typepad.com/blog/2009/07/why-i-use-delphi.html I'd like to know if there are other reasons. Why do you use Delphi? (I'm making this community wiki from the onset. I'm interested in hearing your answers, not in points.)

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  • Modeling software for network serialization protocol design

    - by Aurélien Vallée
    Hello, I am currently designing a low level network serialization protocol (in fact, a refinement of an existing protocol). As the work progress, pen and paper documents start to show their limits: i have tons of papers, new and outdated merged together, etc... And i can't show anything to anyone since i describe the protocol using my own notation (a mix of flow chart & C structures). I need a software that would help me to design a network protocol. I should be able to create structures, fields, their sizes, their layout, etc... and the software would generate some nice UMLish diagrams.

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  • shell script passing arguments

    - by arav
    From the wrapper shell scripts i am calling the Java program. I want the Unix shell script to pass all the arguments to java program except the EMAIL argument. HOW Can i remove the EMAIL argument and pass the rest of the arguments to the java program. EMAIL argument can come at any position. valArgs() { until [ $# -eq 0 ]; do case $1 in -EMAIL) MAILFLAG=Y shift break ;; esac done } main() { valArgs "$@" $JAVA_HOME/bin/java -d64 -jar WEB-INF/lib/test.jar "$@"

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  • What is a monad?

    - by kronoz
    Having briefly looked at Haskell recently I wondered whether anybody could give a brief, succinct, practical explanation as to what a monad essentially is? I have found most explanations I've come across to be fairly inaccessible and lacking in practical detail, so could somebody here help me?

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  • Math/numerical formula every computer programmer should know

    - by aaa
    This is a follow-up question to What should every programmer know and Is mathematics necessary. So the question is, as a computer programmer, what is the most important/useful mathematical or numerical formula that you use? By Formula I mean anything that involves less obvious manipulations, whenever binomial coefficients or bit hacks. I work with multidimensional arrays and various matrix representations. So for me most commonly used formulas are: A(i,j,k,..) = a[i + j*Dim0 + k*Dim0*Dim1 + ... to map indexes to one dimension ( which is basic address calculation which many people do not seem to know). And triangular number T(i) = (i*i + i)/2 which is related to binomial coefficients, used to calculate address in triangular matrixes and many other things. What is your workhorse formula that you think programmer should know?

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  • Is it possible to call a user-space callback function from kernel space in Linux (ioctl)?

    - by Makis
    Is it possible to expand the ioctl interface in Linux so that the user-space application can send a pointer to a function to the kernel space driver? I'm in particular thinking of ways to handle the stream in user-controllable way but doing it in the kernel. Those operations could be attached to the kernel module but this would make development a lot easier as I wouldn't need to mess with the kernel during development. More specifically, this would be the process: Data is read by the driver to a buffer. Data is handled by these user-defined functions in place. Some more handling is done, possibly with some HW blocks. Data is used by a user-space application.

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  • Abstracting boxed array structures in J

    - by estanford
    I've been working on a J function for a while, that's supposed to scan a list and put consecutive copies of an element into separate, concatenated boxes. My efforts have taken me as far as the function (<;. 2) ((2&(~:/\)),1:) which tests successive list entries for inequality, returns a list of boolean values, and cuts the list into boxes that end each time the number 1 appears. Here's an example application: (<;. 2) ((2&(~:/\)),1:) 1 2 3 3 3 4 1 1 1 +-+-+-----+-+-----+ |1|1|0 0 1|1|0 0 1| +-+-+-----+-+-----+ The task would be finished if I could then replace all those booleans with their corresponding values in the input argument. I've been looking for some kind of mystery function that would let me do something like final =: mysteryfunction @ (<;. 2) ((2&(~:/\)),1:) final 1 2 3 3 3 4 1 1 1 +-+-+-----+-+-----+ |1|2|3 3 3|4|1 1 1| +-+-+-----+-+-----+ In an ideal situation, there would be some way to abstractly represent the nesting pattern generated by (<;. 2) ((2&(~:/\)),1:) to the original input list. (i.e. "This boxed array over here has the first element boxed at depth one, the second element boxed at depth one, the third, fourth, and fifth elements boxed together at depth one,..., so take that unboxed list over there and box it up the same way.") I tried fooling around with ;. , S: , L:, L. and &. to produce that behavior, but I haven't had much luck. Is there some kind of operator or principle I'm missing that could make this happen? It wouldn't surprise me if I were overthinking the whole issue, but I'm running out of ideas.

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  • StreamReader.EndOfStream produces IOException

    - by Ziplin
    I'm working on an application that accepts TCP connections and reads in data until an </File> marker is read and then writes that data to the filesystem. I don't want to disconnect, I want to let the client sending the data to do that so they can send multiple files in one connection. I'm using the StreamReader.EndOfStream around my outter loop, but it throws an IOException when the client disconnects. Is there a better way to do this? private static void RecieveAsyncStream(IAsyncResult ar) { TcpListener listener = (TcpListener)ar.AsyncState; TcpClient client = listener.EndAcceptTcpClient(ar); // init the streams NetworkStream netStream = client.GetStream(); StreamReader streamReader = new StreamReader(netStream); StreamWriter streamWriter = new StreamWriter(netStream); while (!streamReader.EndOfStream) // throws IOException { string file= ""; while (file!= "</File>" && !streamReader.EndOfStream) { file += streamReader.ReadLine(); } // write file to filesystem } listener.BeginAcceptTcpClient(RecieveAsyncStream, listener); }

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  • how to use XML sent by html form?

    - by user32167
    i have html form with textarea in which i paste some XML, for example: <network ip_addr="10.0.0.0/8" save_ip="true"> <subnet interf_used="200" name="lan1" /> <subnet interf_used="254" name="lan2" /> </network> When user submit form, that data is send to Java server, so in headers i get something like that: GET /?we=%3Cnetwork+ip_addr%3D%2210.0.0.0%2F8%22+save_ip%3D%22true%22%3E%0D%0A%3Csubnet+interf_used%3D%22200%22+name%3D%22lan1%22+%2F%3E%0D%0A%3Csubnet+interf_used%3D%22254%22+name%3D%22lan2%22+%2F%3E%0D%0A%3C%2Fnetwork%3E HTTP/1.1 how can i use that in my Java applications? I need to make some calculations on that data and re-send new generated XML.

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  • Is it possible to change a exe's icon without recompiling it?

    - by Microkernel
    Hi all, I have lot of executable that I have compiled (long time back) for many of which I don't have sourcecode now. But when I compiled them I didn't put any icons for them, so they all look like same dull, bald default icon. So my questions are, (1) is it possible for me to write a software that can change the resources section of the exe and change its looks? If so, can anyone plz point me to the location where its explained? (I am a beginner, I have no idea on the exe format and all) Also its fun to keep changing Icons without having the pain of recompiling everything just for the icon change... (2) This is raises a natural converse question, Is it similarly possible to zap out the icon used by some file and use it for some other file? (If so, plz point me to location where I can get some details. I am a C/C++ developers and I am looking for solution on Windows Platform... Regards, MicroKernel

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  • More FP-correct way to create an update sql query

    - by James Black
    I am working on access a database using F# and my initial attempt at creating a function to create the update query is flawed. let BuildUserUpdateQuery (oldUser:UserType) (newUser:UserType) = let buf = new System.Text.StringBuilder("UPDATE users SET "); if (oldUser.FirstName.Equals(newUser.FirstName) = false) then buf.Append("SET first_name='").Append(newUser.FirstName).Append("'" ) |> ignore if (oldUser.LastName.Equals(newUser.LastName) = false) then buf.Append("SET last_name='").Append(newUser.LastName).Append("'" ) |> ignore if (oldUser.UserName.Equals(newUser.UserName) = false) then buf.Append("SET username='").Append(newUser.UserName).Append("'" ) |> ignore buf.Append(" WHERE id=").Append(newUser.Id).ToString() This doesn't properly put a , between any update parts after the first, for example: UPDATE users SET first_name='Firstname', last_name='lastname' WHERE id=... I could put in a mutable variable to keep track when the first part of the set clause is appended, but that seems wrong. I could just create an list of tuples, where each tuple is oldtext, newtext, columnname, so that I could then loop through the list and build up the query, but it seems that I should be passing in a StringBuilder to a recursive function, returning back a boolean which is then passed as a parameter to the recursive function. Does this seem to be the best approach, or is there a better one?

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  • Are there any modern platforms with non-IEEE C/C++ float formats?

    - by Patrick Niedzielski
    Hi all, I am writing a video game, Humm and Strumm, which requires a network component in its game engine. I can deal with differences in endianness easily, but I have hit a wall in attempting to deal with possible float memory formats. I know that modern computers have all a standard integer format, but I have heard that they may not all use the IEEE standard for floating-point integers. Is this true? While certainly I could just output it as a character string into each packet, I would still have to convert to a "well-known format" of each client, regardless of the platform. The standard printf() and atod() would be inadequate. Please note, because this game is a Free/Open Source Software program that will run on GNU/Linux, *BSD, and Microsoft Windows, I cannot use any proprietary solutions, nor any single-platform solutions. Cheers, Patrick

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  • Why would a variable in Scala code mysteriously become null?

    - by Alex R
    I've isolated the problem down to this: Predef.println("the value of argv1 here is " + argv(1)); var n: $ = undef; n = argv(1); Predef.println("the value of argv1 here is " + argv(1)); Predef.println("the value of n here is " + n); Predef.println("the class of n here is " + n.getClass); Here's the definition of $: class $ { println("constructed a new $ of type: " + this.getClass); def value: $ = this; def toValue: Value = { new ConstStringValue(this.toString()) }; def -(sym: Symbol): $ = { println("looked up: " + sym); this } def -(sym: $): $ = { println("looked up: " + sym); this } def update(sym: Symbol, any: Any) { println("update called: " + sym + "=" + any); } def apply(sym: Symbol) = { this } def apply(obj: $) = { this } def apply() = { this } def +(o:$) = this.toValue.div(o.toValue) def *(o:$) = this.toValue.mul(o.toValue) def >(o:$) = this.toValue.gt(o.toValue) def <(o:$) = this.toValue.lt(o.toValue) def ++() = { this } def -=(o:$) = { this } } When run, the code prints: the value of argv1 here is 10 the value of argv1 here is 10 the value of n here is null java.lang.NullPointerException at test_1_php$.include(_tmp.scala:149) at php.script.main(php.scala:57) at test_1_php.main(_tmp.scala) [...] Why would n mysteriously lose its value (or fail to take one on)?

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  • 0xDEADBEEF equivalent for 64-bit development?

    - by Peter Mortensen
    For C++ development for 32-bit systems (be it Linux, Mac OS or Windows, PowerPC or x86) I have initialised pointers that would otherwise be undefined (e.g. they can not immediately get a proper value) like so: int *pInt = reinterpret_cast<int *>(0xDEADBEEF); (To save typing and being DRY the right-hand side would normally be in a constant, e.g. BAD_PTR.) If pInt is dereferenced before it gets a proper value then it will crash immediately on most systems (instead of crashing much later when some memory is overwritten or going into a very long loop). Of course the behavior is dependent on the underlying hardware (getting a 4 byte integer from the odd address 0xDEADBEEF from a user process may be perfectly valid), but the crashing has been 100% reliable for all the systems I have developed for so far (Mac OS 68xxx, Mac OS PowerPC, Linux Redhat Pentium, Windows GUI Pentium, Windows console Pentium). For instance on PowerPC it is illegal (bus fault) to fetch a 4 byte integer from an odd address. What is a good value for this on 64-bit systems?

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  • what is pagecache page

    - by kumar
    /* * Each physical page in the system has a struct page associated with * it to keep track of whatever it is we are using the page for at the * moment. Note that we have no way to track which tasks are using * a page, though if it is a pagecache page, rmap structures can tell us * who is mapping it. */ include/linux/mm_types.h Here Please lemme know what is "pagecache page" means? Thanks!

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