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• How does Subnetting Work?

  - by Kyle Brandt

  How does Subnetting Work, and How do you do it by hand or in your head? Can someone explain both conceptually and with several examples? Server Fault gets lots of subnetting homework questions, so we could use an answer to point them to on Server Fault itself. What is classless routing and why is class-based routing obsolete? If I have a network, how do I figure out how to split it up? If I am given a netmask, how do I know what the network Range is for it? Sometimes there is a slash followed by a number, what is that number? Sometimes there is a subnet mask, but also a wildcard mask, they seem like the same thing but they are different? Someone mentioned something about knowing binary for this? What is NAT (Network Address Translation). Not looking for links to other sites (unless maybe you have one post with a bunch of good ones). I already know how to subnet, I just thought it would be nice if Server Fault had a generic subnetting answer.

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• Help improving a simple assembly function

  - by MPelletier

  I just handed in this function in an assignment. It is done (hence no homework tag). But I would like to see how this can be improved. Essentially, the function sums the squares of all the integers between 1 and the given number, using the following formula: n(n+1)(2n+1)/6 Where n is the maximum number. The function below is made to catch any overflow and return 0 should any occur. UInt32 sumSquares(const UInt32 number) { int result = 0; __asm { mov eax, number //move number in eax mov edx, 2 //move 2 in edx mul edx //multiply (2n) jo end //jump to end if overflow add eax, 1 //addition (2n+1) jo end //jump to end if overflow mov ecx, eax //move (2n+1) in ecx mov ebx, number //move number in ebx add ebx, 1 //addition (n+1) jo end //jump to end if overflow mov eax, number //move number in eax for multiplication mul ebx //multiply n(n+1) jo end //jump to end if overflow mul ecx //multiply n(n+1)(2n+1) jo end //jump to end if overflow mov ebx, 6 //move 6 in ebx div ebx //divide by 6, the result will be in eax mov result, eax //move eax in result end: } return result; } Basically, I want to know what I can improve in there. In terms of best-practices mostly. One thing sounds obvious: smarter overflow check (with a single check for whatever maximum input would cause an overflow).

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• Nested WHILE loops in Python

  - by Guru

  I am a beginner with Python and trying few programs. I have something like the following WHILE loop construct in Python (not exact). IDLE 2.6.4 >>> a=0 >>> b=0 >>> while a < 4: a=a+1 while b < 4: b=b+1 print a, b 1 1 1 2 1 3 1 4 I am expecting the outer loop to loop through 1,2,3 and 4. And I know I can do this with FOR loop like this >>> for a in range(1,5): for b in range(1,5): print a,b 1 1 1 2 1 3 1 4 2 1 2 2 2 3 2 4 3 1 3 2 3 3 3 4 4 1 4 2 4 3 4 4 But, what is wrong with WHILE loop? I guess I am missing some thing obvious, but could not make out. P.S: Searched out SO, found few questions but none as close to this. Don't know whether this could classified as homework, the actual program was different, the problem is what puzzles me.

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• error C2109: subscript requires array or pointer type

  - by numerical25

  I am trying to debug some homework but I am having trouble with these lines of code #include "stdafx.h" #include<conio.h> #include<iostream> #include<string> using namespace std; int main() { char word; cout << "Enter a word and I will tell you whether it is" << endl << "in the first or last half of the alphabet." << endl << "Please begin the word with a lowercase letter. --> "; cin >> word; if(word[0] >= 'm') cout << word << " is in the first half of the alphabet" << endl; else cout << word << " is in the last half of the alphabet" << endl; return 0; } I get the following error and I have no clue what its sayings error C2109: subscript requires array or pointer type

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• Detect a white square in a black and white image

  - by gcc

  I saw that question i one web site (cite name like that programm.) then i tried to solve but icannot (not my and myfriend homework ) how can i approach to that one (in program.net no solution there is ) Read black & white image data from standard input, and detect a white square in the image. Output the coordinates of the upper left corner of the square, and the width of the square. In the preliminary work, you can print the output and terminate your program after you detect your first square. If you can't find any square on the image, you will print the string: "NO DETECTION". Input (which represents a 2 by 2 square in the center of a 5 by 4 image): 2 2 5 4 0 0 0 0 0 0 0 255 255 0 0 0 255 255 0 0 0 0 0 0 Output: 3 2 2 Input (more comprehensible format of the image, with the same output): 2 6 4 000 000 000 000 000 000 000 000 255 255 255 000 000 000 000 255 255 000 000 000 000 000 000 000 Output: no detection Input can be: 000 255 255 000 000 000 000 255 255 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 255 255 255 000 000 000 255 255 255 000 000 000 255 255 255 000 000 000 000 000 000 000 If there are two squares detected, we should use the biggest one

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• Access Violation When Writing Dynamic 2D Array... Sometimes

  - by Shraptnel

  This program is meant to generate a dynamic array, however it gives an access violation error when writing when given certain dimensions. Eg: R = 6, C = 5 crashes, but then R = 5, C = 6 doesn't. In case your wondering, it isn't my homework to "fix" this broken program, this is the method we were taught in class. Also part of my assessment is to use this method, so vectors are out. Thanks in advance! #include <iostream> using namespace std; int main(){ const int R = 6; const int C = 5; char **d; d = new char *[R]; for(int i=0; i<C; ++i){ d[i] = new char[C]; } //initialise for(int i=0; i<R; ++i){ for(int j=0; j<C; ++j){ d[i][j] = 'd'; cout<<d[i][j]; } cout<<endl; } cout<<endl; system("pause"); return 0; }

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• Project ideas for automated deduction/automated theorem proving?

  - by wsh

  Dear Stack Overflow brethren, I'm a second-semester junior who will embark upon my thesis soon, and I have an interest in automated deduction and automated theorem provers. As in, I'd like to advance the art in some way (I don't mean that pretentiously, but I do want to do something productive). I've Googled pretty far and wide and so far few promising ideas have emerged. There are a few student project idea pages, but most seem either horribly outdated or too advanced (I was originally going to attempt to synthesize postmodernist thought (hahaha) and abstract its logical content, build a complete and consistent model (if possible, of course), and attempt to automate it, grounding said model as possible in a nonstandard logic a la these. My advisor thought that gave postmodernist thought too much credit (a while ago I reimplemented the Postmodernism Generator in Haskell with Parsec, so that is in part where the idea came from); I am tempted to concur.) So, yeah. Does anyone have ideas? I apologize if there is some obvious gap in my approach here/if I haven't appropriately done my homework (and if there is one, please tell me!), but in large part I don't even know where to start, and thank you for reading all that.

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• Is any solution the correct solution?

  - by Eli

  I always think to myself after solving a programming challenge that I have been tied up with for some time, "It works, thats good enough". I don't think this is really the correct mindset, in my opinion and I think I should always be trying to code with the greatest performance. Anyway, with this said, I just tried a ProjectEuler question. Specifically question #2. How could I have improved this solution. I feel like its really verbose. Like I'm passing the previous number in recursion. <?php /* Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ... Find the sum of all the even-valued terms in the sequence which do not exceed four million. */ function fibonacci ( $number, $previous = 1 ) { global $answer; $fibonacci = $number + $previous; if($fibonacci > 4000000) return; if($fibonacci % 2 == 0) { $answer = is_numeric($answer) ? $answer + $fibonacci : $fibonacci; } return fibonacci($fibonacci, $number); } fibonacci(1); echo $answer; ?> Note this isn't homework. I left school hundreds of years ago. I am just feeling bored and going through the Project Euler questions

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• Concat LPSTR in C++

  - by Cat Man Do

  Trying to use as basic C++ as I can to build a list of numbers from 1-52 in a random order (deck of cards). Unfortauntely, all my attempts to concat the strings and get a result end in failure. Any suggestions? NOTE: This is not homework it's something I'm using to create a game. // Locals char result[200] = ""; // Result int card[52]; // Array of cards srand(time(0)); // Initialize seed "randomly" // Build for (int i=0; i<52; i++) { card[i] = i; // fill the array in order } // Shuffle cards for (int i=0; i<(52-1); i++) { int r = i + (rand() % (52-i)); int temp = card[i]; card[i] = card[r]; card[r] = temp; } // Build result for (int c=0; c<52; c++) { // Build sprintf(result, "%d", card[c]); // Comma? if ( c < 51 ) { sprintf(result, "%s", ","); } } My end result is always garbled text. Thanks for the help.

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• Multiplication algorithm for abritrary precision (bignum) integers.

  - by nn

  Hi, I'm writing a small bignum library for a homework project. I am to implement Karatsuba multiplication, but before that I would like to write a naive multiplication routine. I'm following a guide written by Paul Zimmerman titled "Modern Computer Arithmetic" which is freely available online. On page 4, there is a description of an algorithm titled BasecaseMultiply which performs gradeschool multiplication. I understand step 2, 3, where B^j is a digit shift of 1, j times. But I don't understand step 1 and 3, where we have A*b_j. How is this multiplication meant to be carried out if the bignum multiplication hasn't been defined yet? Would the operation "*" in this algorithm just be the repeated addition method? Here is the parts I have written thus far. I have unit tested them so they appear to be correct for the most part: The structure I use for my bignum is as follows: #define BIGNUM_DIGITS 2048 typedef uint32_t u_hw; // halfword typedef uint64_t u_w; // word typedef struct { unsigned int sign; // 0 or 1 unsigned int n_digits; u_hw digits[BIGNUM_DIGITS]; } bn; Currently available routines: bn *bn_add(bn *a, bn *b); // returns a+b as a newly allocated bn void bn_lshift(bn *b, int d); // shifts d digits to the left, retains sign int bn_cmp(bn *a, bn *b); // returns 1 if a>b, 0 if a=b, -1 if a<b

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• Passing string with (accidental) escape character loses character even though it's a raw string

  - by Steen

  I have a function with a python doctest that fails because one of the test input strings has a backslash that's treated like an escape character even though I've encoded the string as a raw string. My doctest looks like this: >>> infile = [ "Todo: fix me", "/** todo: fix", "* me", "*/", r"""//\todo stuff to fix""", "TODO fix me too", "toDo bug 4663" ] >>> find_todos( infile ) ['fix me', 'fix', 'stuff to fix', 'fix me too', 'bug 4663'] And the function, which is intended to extract the todo texts from a single line following some variation over a todo specification, looks like this: todos = list() for line in infile: print line if todo_match_obj.search( line ): todos.append( todo_match_obj.search( line ).group( 'todo' ) ) And the regular expression called todo_match_obj is: r"""(?:/{0,2}\**\s?todo):?\s*(?P<todo>.+)""" A quick conversation with my ipython shell gives me: In [35]: print "//\todo" // odo In [36]: print r"""//\todo""" //\todo And, just in case the doctest implementation uses stdout (I haven't checked, sorry): In [37]: sys.stdout.write( r"""//\todo""" ) //\todo My regex-foo is not high by any standards, and I realize that I could be missing something here. EDIT: Following Alex Martellis answer, I would like suggestions on what regular expression would actually match the blasted r"""//\todo fix me""". I know that I did not originally ask for someone to do my homework, and I will accept Alex's answer as it really did answer my question (or confirm my fears). But I promise to upvote any good solutions to my problem here :) I'm using Python 2.6.4 (r264:75706, Dec 7 2009, 18:45:15) Thank you for reading this far (If you skipped directly down here, I understand)

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• Python: Seeing all files in Hex.

  - by Recursion

  I am writing a python script which looks at common computer files and examines them for similar bytes, words, double word's. Though I need/want to see the files in Hex, ande cannot really seem to get python to open a simple file in python. I have tried codecs.open with hex as the encoding, but when I operate on the file descriptor it always spits back File "main.py", line 41, in <module> main() File "main.py", line 38, in main process_file(sys.argv[1]) File "main.py", line 27, in process_file seeker(line.rstrip("\n")) File "main.py", line 15, in seeker for unit in f.read(2): File "/usr/lib/python2.6/codecs.py", line 666, in read return self.reader.read(size) File "/usr/lib/python2.6/codecs.py", line 472, in read newchars, decodedbytes = self.decode(data, self.errors) File "/usr/lib/python2.6/encodings/hex_codec.py", line 50, in decode return hex_decode(input,errors) File "/usr/lib/python2.6/encodings/hex_codec.py", line 42, in hex_decode output = binascii.a2b_hex(input) TypeError: Non-hexadecimal digit found def seeker(_file): f = codecs.open(_file, "rb", "hex") for LINE in f.read(): print LINE f.close() I really just want to see files, and operate on them as if it was in a hex editor like xxd. Also is it possible to read a file in increments of maybe a word at a time. No this is not homework.

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• Simple Java calculator

  - by Kevin Duke

  Firstly this is not a homework question. I am practicing my knowledge on java. I figured a good way to do this is to write a simple program without help. Unfortunately, my compiler is telling me errors I don't know how to fix. Without changing much logic and code, could someone kindly point out where some of my errors are? Thanks import java.lang.*; import java.util.*; public class Calculator { private int solution; private int x; private int y; private char operators; public Calculator() { solution = 0; Scanner operators = new Scanner(System.in); Scanner operands = new Scanner(System.in); } public int addition(int x, int y) { return x + y; } public int subtraction(int x, int y) { return x - y; } public int multiplication(int x, int y) { return x * y; } public int division(int x, int y) { solution = x / y; return solution; } public void main (String[] args) { System.out.println("What operation? ('+', '-', '*', '/')"); System.out.println("Insert 2 numbers to be subtracted"); System.out.println("operand 1: "); x = operands; System.out.println("operand 2: "); y = operands.next(); switch(operators) { case('+'): addition(operands); operands.next(); break; case('-'): subtraction(operands); operands.next(); break; case('*'): multiplication(operands); operands.next(); break; case('/'): division(operands); operands.next(); break; } } }

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• Bison input analyzer - basic question on optional grammer and input interpretation

  - by kumar_m_kiran

  Hi All, I am very new to Flex/Bison, So it is very navie question. Pardon me if so. May look like homework question - but I need to implement project based on below concept. My question is related to two parts, Question 1 In Bison parser, How do I provide rules for optional input. Like, I need to parse the statment Example : -country='USA' -state='INDIANA' -population='100' -ratio='0.5' -comment='Census study for Indiana' Here the ratio token can be optional. Similarly, If I have many tokens optional, then How do I provide the grammer in the parser for the same? My code looks like, %start program program : TK_COUNTRY TK_IDENTIFIER TK_STATE TK_IDENTIFIER TK_POPULATION TK_IDENTIFIER ... where all the tokens are defined in the lexer. Since there are many tokens which are optional, If I use "|" then there will be many different ways of input combination possible. Question 2 There are good chance that the comment might have quotes as part of the input, so I have added a token -tag which user can provide to interpret the same, Example : -country='USA' -state='INDIANA' -population='100' -ratio='0.5' -comment='Census study for Indiana$'s population' -tag=$ Now, I need to reinterpret Indiana$'s as Indiana's since -tag=$. Please provide any input or related material for to understand these topic. Thanks for your input in advance.

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• what data structure should I use for hash lookup as well as binary search?

  - by zebraman

  I am working on a school homework. I have a list of names. I want to be able to perform binary search on these names (find all names between a lower and upper bound) for first name as well as last name, and perform keyword searches as well (this will be accomplished using hashing. For example, if I have the names Garfield Cat Snoopy Dog Captain Crunch Fat Cat then a binary search of first names (C,H) will return Captain Crunch, Fat Cat, and Garfield Cat. A binary search of last names (Cr,D) will return Captain Crunch. A keyword search of 'cat' will return Fat Cat and Garfield Cat. I understand binary search will only work on a sorted list, but since I am planning on searching two different criteria, I will have to sort the list by last name or first name depending on what I'm searching for. I feel like it will be too inefficient to have to resort the list each time I want to perform a new binary search. Would it just be better for me to set up and maintain two sorted lists (one for sorted by first name, one for sorted by last name)? Also, for hashing, will I have to set up a different table of names for that as well? I understand each keyword will hash to some value determined by a hash function, and this value (or key) is a table address where the corresponding names are stored. So I just want to know what would be the best way to solve this problem? Maintaining separate structures, or is there a way to efficiently do everything I want with just one data structure?

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• priority queue with limited space: looking for a good algorithm

  - by SigTerm

  This is not a homework. I'm using a small "priority queue" (implemented as array at the moment) for storing last N items with smallest value. This is a bit slow - O(N) item insertion time. Current implementation keeps track of largest item in array and discards any items that wouldn't fit into array, but I still would like to reduce number of operations further. looking for a priority queue algorithm that matches following requirements: queue can be implemented as array, which has fixed size and _cannot_ grow. Dynamic memory allocation during any queue operation is strictly forbidden. Anything that doesn't fit into array is discarded, but queue keeps all smallest elements ever encountered. O(log(N)) insertion time (i.e. adding element into queue should take up to O(log(N))). (optional) O(1) access for *largest* item in queue (queue stores *smallest* items, so the largest item will be discarded first and I'll need them to reduce number of operations) Easy to implement/understand. Ideally - something similar to binary search - once you understand it, you remember it forever. Elements need not to be sorted in any way. I just need to keep N smallest value ever encountered. When I'll need them, I'll access all of them at once. So technically it doesn't have to be a queue, I just need N last smallest values to be stored. I initially thought about using binary heaps (they can be easily implemented via arrays), but apparently they don't behave well when array can't grow anymore. Linked lists and arrays will require extra time for moving things around. stl priority queue grows and uses dynamic allocation (I may be wrong about it, though). So, any other ideas?

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• Modeling related objects and their templates

  - by Duddle

  Hello everybody! I am having trouble correctly modeling related objects that can use templates. This is not homework, but part of a small project in the university. In this application the user can add several elements, which can either be passive or active. Each concrete element has different attributes, these must be set by the user. See diagram 1: Since the user will create many elements, we want there to be templates for each type of element, so some of the attributes are filled in automatically. See diagram 2: In my opinion, this is a bad design. For example, to get all possible templates for a PassiveElementA-object, there has to be a list/set somewhere that only holds PassiveElementATemplate-objects. There has to be a separate list for each subclass of Element. So if you wanted to add a new PassiveElement-child, you also have to edit the class which holds all these separate lists. I cannot figure out a good way to solve this problem. Since the concrete classes (i.e. PassiveElementA, ..., PassiveElementZ) have so many different attributes, many of the design patterns I know do not work. Thanks in advance for any hints, and sorry for my bad English.

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• Java SSH2 libraries in depth: Trilead/Ganymed/Orion [/other?]

  - by Bernd Haug

  I have been searching for a pure Java SSH library to use for a project. The single most important needed feature is that it has to be able to work with command-line git, but remote-controlling command-line tools is also important. A pretty common choice, e.g. used in the IntelliJ IDEA git integration (which works very well), seems to be Trilead SSH2. Looking at their website, it's not being maintained any more. Trilead seems to have been a fork of Ganymed SSH2, which was a ETH Zurich project that didn't see releases for a while, but had a recent release by its new owner, Christian Plattner. There is another actively maintained fork from that code base, Orion SSH, that saw an even more recent release, but which seems to get mentioned online much less than the other 2 forks. Has anybody here worked with any of (or, if possible, both) of Ganymed and Orion and could kindly describe the development experience with either/both? Accuracy of documentation [existence of documentation?], stability, buggyness... - all of these would be highly interesting to me. Performance is not so important for my current project. If there is another pure-Java SSH implementation that should be used instead, please feel free to mention it, but please don't just mention a name...describe your judgment from actual experience. Sorry if this question may seem a bit "do my homework"-y, but I've really searched for reviews. Everything out there seems to be either a listing of implementations or short "use this! it's great!" snippets.

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• Git as mercurial client? Why no git-hg?

  - by aapeli

  This is a question that's been bothering me for a while. I've done my homework and checked stackoverflow and found at least these two topics about my question: Git for Mercurial like git-svn and Git interoperability with a Mercurial repository I've done some serious googling to solve this issue, but so far with no luck. I've also read the Git Internals book, and the Mercurial Definitive Behind the Scenes to try to figure this out. I'm still a bit puzzled why I haven't been able to find any suitable git-hg type of a tool. From my perspective hg-svn is one of the main features, why I've chosen to use git over mercurial also at work. It allows me to use a workflow I like, and nobody else needs to bother, if they don't care. I just don't see the point in using the intermediate hg repo to convert back and forth, as suggested in one of the chains. So anyway, from what I've read hg and git seem very similar in conceptual design. There are differences under the hood, but none of those should prevent creating a git client for hg. As it seems to me, remote tracking branches and octopus merges make git even more powerful than hg is. So, the real question, is there any real reason why git-hg does not exist (or at least is very hard to find)? Is there some animosity from git users (and developers) towards their hg counterparts that has caused the lack of the git-hg tool? Do any of you have any plans to develop something like this, and go public with it? I could volunteer (although with very feeble C-skills) to participate to get this done. I just don't possess the full knowledge to start this up myself. Could this be the tool to end all DVCS wars for good?

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• Modify request querystring paramaters to build a new link without resorting to string manipulation

  - by Andrew M

  Hi All, I want to dynamically populate a link with the URI of the current request, but set one specific query string parameter. All other querystring paramaters (if there are any) should be left untouched. And I don't know in advance what they might be. Eg, imagine I want to build a link back to the current page, but with the querystring parameter "valueOfInterest" always set to be "wibble" (I'm doing this from the code-behind of an aspx page, .Net 3.5 in C# FWIW). Eg, a request for either of these two: /somepage.aspx /somepage.aspx?valueOfInterest=sausages would become: /somepage.aspx?valueOfInterest=wibble And most importantly (perhaps) a request for: /somepage.aspx?boring=something /somepage.aspx?boring=something&valueOfInterest=sausages would preserve the boring params to become: /somepage.aspx?boring=something&valueOfInterest=wibble Caveats: I'd like to avoid string manipulation if there's something more elegant in asp.net that is more robust. However if there isn't something more elegant, so be it. I've done (a little) homework: I found a blog post which suggested copying the request into a local HttpRequest object, but that still has a read-only collection for the querystring params. I've also had a look at using a URI object, but that doesn't seem to have a querystring

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• Delete element from Set

  - by Blitzkr1eg

  Hi. I have 2 classes Tema(Homework) and Disciplina (course), where a Course has a Set of homeworks. In Hibernate i have mapped this to a one-to-many associations like this: <class name="model.Disciplina" table="devgar_scoala.discipline" > <id name="id" > <generator class="increment"/> </id> <set name="listaTeme" table="devgar_scoala.teme"> <key column="Discipline_id" not-null="true" ></key> <one-to-many class="model.Tema" ></one-to-many> </set> </class> <class name="model.Tema" table="devgar_scoala.teme" > <id name="id"> <generator class="increment" /> </id> <property name="titlu" type="string" /> <property name="cerinta" type="binary"> <column name="cerinta" sql-type="blob" /> </property> </class> The problem is that it will add (insert rows in the table 'Teme') but it won't delete any rows and i get no exceptions thrown. Im using the merge() method.

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• Pointer incrementing query

  - by Craig

  I have been looking at this piece of code, and it is not doing what I expect. I have 3 globals. int x, y, *pointer, z; Inside of main I declare them. x = 10; y = 25; pointer = &x; now at this point &x is 0x004A144 &y is 0x004A138 pointer is pointing to 0x004A144 Now when I increment: y = *++pointer; it points to 0x004A148, this is the address y should be at shouldn't it? The idea is that incrementing the pointer to 'x' should increment it to point at y, but it doesn't seem to want to declare them in in order like I expect. If this a VS2005 / 2008 problem? Or maybe an Express problem? This isn't really homework, as I have done it a couple of years ago but I was revising on my pointer stuff and I tried this again. But this time I am getting unexpected results. Does anyone have opinions on this? *UPDATE sorry should be more clear, 'thought' on declaration 'y' should be at 148, and that incrementing the pointer pointing to x should increment 'pointer' to 148 (which it does), but that isn't where y is. Why isn't y declaring where it should be.

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• Java semaphore to syncronize printing to screen

  - by Travis Griswald

  I'm currently stuck on a bit of homework and was wondering if anyone could help - I have to use semaphores in java to syncronize printing letters from 2 threads - one printing "A" and one printing "B". I cannot print out more than 2 of the same character in a row, so output should look like AABABABABABBABABABABAABBAABBABABA At the moment I have 3 semaphores, a binary mutex set to 1, and a counting semaphore, and my thread classes look something like this - public void run() { while (true) { Time.delay(RandomGenerator.integer(0,20)); Semaphores.mutex.down (); System.out.println (produce()); if (printCount > 1) { printCount = 0; Semaphores.mutex.up (); Semaphores.printB.up(); } } } public String produce() { printCount++; return "A"; } public void run() { while (true) { Time.delay(RandomGenerator.integer(0,20)); Semaphores.mutex.down (); System.out.println (produce()); if (printCount > 1) { printCount = 0; Semaphores.mutex.up (); Semaphores.printA.up(); } } } public String produce() { printCount++; return "B"; } Yet whatever I try it either deadlocks, or it seems to be working only printing 2 in a row at most, but always seems to print 3 in a row every now and again! Any help is much appreciated, not looking code or anything just a few pointers if possible :)

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• String Manipulation in C

  - by baris_a

  Hi guys, I am helping my nephew for his C lab homework, it is a string manipulation assignment and applying Wang's algorithm. Here is the BNF representation for the input. <sequent> ::= <lhs> # <rhs> <lhs> ::= <formulalist>| e <rhs> ::= <formulalist>| e <formulalist> ::= <formula>|<formula> , <formulalist> <formula> ::= <letter>| - <formula>| (<formula><in?xop><formula>) <in?xop> ::= & | | | > <letter> ::= A | B | ... | Z What is the best practice to handle and parse this kind of input in C? How can I parse this structure without using struct? Thanks in advance.

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• Python optimization problem?

  - by user342079

  Alright, i had this homework recently (don't worry, i've already done it, but in c++) but I got curious how i could do it in python. The problem is about 2 light sources that emit light. I won't get into details tho. Here's the code (that I've managed to optimize a bit in the latter part): import math, array import numpy as np from PIL import Image size = (800,800) width, height = size s1x = width * 1./8 s1y = height * 1./8 s2x = width * 7./8 s2y = height * 7./8 r,g,b = (255,255,255) arr = np.zeros((width,height,3)) hy = math.hypot print 'computing distances (%s by %s)'%size, for i in xrange(width): if i%(width/10)==0: print i, if i%20==0: print '.', for j in xrange(height): d1 = hy(i-s1x,j-s1y) d2 = hy(i-s2x,j-s2y) arr[i][j] = abs(d1-d2) print '' arr2 = np.zeros((width,height,3),dtype="uint8") for ld in [200,116,100,84,68,52,36,20,8,4,2]: print 'now computing image for ld = '+str(ld) arr2 *= 0 arr2 += abs(arr%ld-ld/2)*(r,g,b)/(ld/2) print 'saving image...' ar2img = Image.fromarray(arr2) ar2img.save('ld'+str(ld).rjust(4,'0')+'.png') print 'saved as ld'+str(ld).rjust(4,'0')+'.png' I have managed to optimize most of it, but there's still a huge performance gap in the part with the 2 for-s, and I can't seem to think of a way to bypass that using common array operations... I'm open to suggestions :D

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