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• Best approach for using Scanner Objects in Java?

  - by devjeetroy

  Although I'm more of a C++/ASM guy, I have to work with java as a part of my undergrad course at college. Our teacher taught us input using Scanner(System.in), and told us that if multiple functions are were taking user input, it would be advisable that a single Scanner object is passed around so as to reduce chances of the input stream getting screwed up. Now using this approach has gotten me into a situation where I'm trying to use a Scanner.nextLine(), and this statement does not wait for user input. It just moves on to the following statement. I figured there may be some residual cr/lf or other characters in the Scanner that might not have been retrieved are causing the problem. Here is the code. while(lineScanner.hasNext()) { if(isPlaceHolder(temp = lineScanner.next())) { temp = temp.replace("<",""); temp = temp.replace(">", ""); System.out.print("Enter "+aOrA(temp.charAt(0)) +" " +temp + " : "); temp = consoleInput.nextLine(); } outputFileStream.print(temp + " "); } All of the code is inside a function which receives a Scanner object consoleInput. Ok, so what happens when i run it is that when the program enters the if() the first time, It carries out theSystem.out.print, does not wait for user input, and moves on to the second time that it enters the 'if' block. This time, it takes the input and the rest of the program operates normally. What is even more surprising is that when i check the output file created by the program, it is perfect, just as i want to be. Almost as if the first time input using the scanner is correct. I have solved this problem by creating a new system.in Scanner in the function itself, instead of receiving the Scanner object as a parameter. But I am still very curious to know what the hell is happening and why it couldn't be solved using a simple Scanner.reset(). Would it be better to just simply create a Scanner Object for each function? Thanks, Devjeet PS. Although I know how to take input using fileinputstreams and the like, we are not supposed to use it with the homework.

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• Syntax error while copying an multidimensional array to another in C

  - by mantuko

  We are programming a ST269 microcontroller which has two IR distance sensors. To calibrate these sensors we made one table for each sensor with the distance we measured and the corresponding value we get from the ADC. Now we want to use one function to approximate the values in between. So we defined two two-dimensional arrays (one for each sensor) as global variables. In our function we then want to copy the one array we want to work with to a working array and approximate our values. So here's the code: ... unsigned int ir_werte_re[][] = { {8,553}, ... {83,133} }; unsigned int ir_werte_li[][] = { {8,566}, ... {83,147} }; ... unsigned int geradenaproximation(unsigned int messwert, unsigned int seite) { unsigned int working_array[16][16]; unsigned int i = 0; if (seite == 0) { for (i = 0; i < sizeof(working_array); i++) { working_array[i][0] = ir_werte_li[i][0]; i++; } } else { for (i = 0; i < sizeof(working_array); i++) { working_array[i][0] = ir_werte_re[i][0]; i++; } } i = 0; unsigned int y1 = 0; unsigned int x1 = 0; ... } This code is in a file called sensor.c. We didn't write anything about our global arrays in the sensor.h should we? The sensor.h of course is included in our main.c and there the function is called. We also tried to copy the arrays via memcpy(working_array, ir_werte_li, sizeof(working_array)); And in every way we do this we get a syntax error near unsigned in the line where we're declaring unsigned int y1 = 0; and I'm pretty sure that there is no syntax error in this line : ) The last time I spend coding in C is a few years away so I'm not sure if the way we try to do this is good. Perhaps we can solve this by using a pointer instead of really copying the array or something. So please help me out I'll appreciate your bits on this.

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• How should I handle the case in which a username is already in use?

  - by idealmachine

  I'm a JavaScript programmer and new to PHP and MySQL (want to get into server-side coding). Because I'm trying to learn PHP by building a simple online game (more specifically, correspondence chess), I'm starting by implementing a simple user accounts system. Of course, user registration comes first. What are the best practices for: How I should handle the (likely) possibility that when a user tries to register, the username he has chosen is already in use, particularly when it comes to function return values?($result === true is rather ugly, and I'm not sure whether checking the MySQL error code is the best way to do it either) How to cleanly handle varying page titles?($gPageTitle = '...'; require_once 'bgsheader.php'; is also rather ugly) Anything else I'm doing wrong? In some ways, PHP is rather different from JavaScript... Here is a (rather large) excerpt of the code I have written so far. Note that this is a work in progress and is missing security checks that I will add as my next step. function addUser( $username, $password ) { global $gDB, $gPasswordSalt; $stmt = $gDB->prepare( 'INSERT INTO user(user_name, user_password, user_registration) VALUES(?, ?, NOW())' ); $stmt || trigger_error( 'Failed to prepare statement: ' . htmlspecialchars( $gDB->error ) ); $hashedPassword = hash_hmac( 'sha256', $password, $gPasswordSalt, true ); $stmt->bind_param( 'ss', $username, $hashedPassword ); if( $stmt->execute() ) { return true; } elseif( $stmt->errno == 1062) { return 'exists'; } else { trigger_error( 'Failed to execute statement: ' . htmlspecialchars( $stmt->error ) ); } } $username = $_REQUEST['username']; $password = $_REQUEST['password']; $result = addUser( $username, $password ); if( $result === true ) { $gPageTitle = 'Registration successful'; require_once 'bgsheader.php'; echo '<p>You have successfully registered as ' . htmlspecialchars( $username ) . ' on this site.</p>'; } elseif( $result == 'exists' ) { $gPageTitle = 'Username already taken'; require_once 'bgsheader.php'; echo '<p>Someone is already using the username you have chosen. Please try using another one instead.'; } else { trigger_error('This should never happen'); } require_once 'bgsfooter.php';

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• organizing external libraries and include files

  - by stijn

  Over the years my projects use more and more external libraries, and the way I did it starts feeling more and more awkward (although, that has to be said, it does work flawlessly). I use VS on Windows, CMake on others, and CodeComposer for targetting DSPs on Windows. Except for the DSPs, both 32bit and 64bit platforms are used. Here's a sample of what I am doing now; note that as shown, the different external libraries themselves are not always organized in the same way. Some have different lib/include/src folders, others have a single src folder. Some came ready-to-use with static and/or shared libraries, others were built /path/to/projects /projectA /projectB /path/to/apis /apiA /src /include /lib /apiB /include /i386/lib /amd64/lib /path/to/otherapis /apiC /src /path/to/sharedlibs /apiA_x86.lib -->some libs were built in all possible configurations /apiA_x86d.lib /apiA_x64.lib /apiA_x64d.lib /apiA_static_x86.lib /apiB.lib -->other libs have just one import library /path/to/dlls -->most of this directory also gets distributed to clients /apiA_x86.dll and it's in the PATH /apiB.dll Each time I add an external libary, I roughly use this process: build it, if needed, for different configurations (release/debug/platform) copy it's static and/or import libraries to 'sharedlibs' copy it's shared libraries to 'dlls' add an environment variable, eg 'API_A_DIR' that points to the root for ApiA, like '/path/to/apis/apiA' create a VS property sheet and a CMake file to state include path and eventually the library name, like include = '$(API_A_DIR)/Include' and lib = apiA.lib add the propertysheet/cmake file to the project needing the library It's especially step 4 and 5 that are bothering me. I am pretty sure I am not the only one facing this problem, and would like see how others deal with this. I was thinking to get rid of the environment variables per library, and use just one 'API_INCLUDE_DIR' and populating it with the include files in an organized way: /path/to/api/include /apiA /apiB /apiC This way I do not need the include path in the propertysheets nor the environment variables. For libs that are only used on windows I even don't need a propertysheet at all as I can use #pragmas to instruct the linker what library to link to. Also in the code it will be more clear what gets included, and no need for wrappers to include files having the same name but are from different libraries: #include <apiA/header.h> #include <apiB/header.h> #include <apiC_version1/header.h> The withdrawal is off course that I have to copy include files, and possibly** introduce duplicates on the filesystem, but that looks like a minor price to pay, doesn't it? ** actually once libraries are built, the only thing I need from them is the include files and thie libs. Since each of those would have a dedicated directory, the original source tree is not needed anymore so can be deleted..

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• C++Template in Java?

  - by RnMss

  I want something like this: public abstract class ListenerEx<LISTENER, PARENT> implements LISTENER { PARENT parent; public ListenerEx(PARENT p) { parent = p; } } But it doesn't compile. Is there a better solution? Is there something in Java like C++ template that would do check syntax after template deduction? The following explains why I need such a ListenerEX class, if you already know what it is, you don't need to read the following. I have a main window, and a button on it, and I want to get access to some method of the main window's within the listener: public class MainWindow extends JFrame { public void doSomething() { /* ... */ } public void doSomethingElse() { /* ... */ } private JButton button; public MainWindow() { button = new JButton(...); add(button); button.setActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { doSomething(); doSomethingElse(); } }); } } This would compile but does not work properly all the time. (Why would it compile when the ActionListener does not have doSomething() method?) Of course we can do it like this: public class MainWindow extends JFrame { public void doSomething() { } public void doSomethingElse() { } private JButton button; public MainWindow() { button = new JButton(...); add(button); class ActionListener1 implements ActionListener { MainWindow parent; public ActionListener(MainWindow p) { parent = p; } public void actionPerformed(ActionEvent e) { parent.doSomething(); parent.doSomethingElse(); } } button.setActionListener(new ActionListener1(this)); } } However I hate this style ... So I tried: public abstract class ActionListenerEx<P> implements ActionListener { P parent; public ActionListenerEx(P p) { parent = p; } } public class MainWindow extends JFrame { public void doSomething() { } public void doSomethingElse() { } private JButton button; public MainWindow() { button = new JButton(...); add(button); button.setActionListener(new ActionListenerEx<MainWindow>(this) { public void actionPerformed(ActionEvent e) { parent.doSomething(); parent.doSomethingElse(); } }); } } But there's lots of Listeners beside the ActionListener ... public abstract class ActionListenerEx<LISTENER, PARENT> implements LISTENER { PARENT parent; public ActionListenerEx(PARENT p) { parent = p; } } However, it won't compile ... I am fresh at Java, and I wonder if there's already better solution.

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• Simplifying const Overloading?

  - by templatetypedef

  Hello all- I've been teaching a C++ programming class for many years now and one of the trickiest things to explain to students is const overloading. I commonly use the example of a vector-like class and its operator[] function: template <typename T> class Vector { public: T& operator[] (size_t index); const T& operator[] (size_t index) const; }; I have little to no trouble explaining why it is that two versions of the operator[] function are needed, but in trying to explain how to unify the two implementations together I often find myself wasting a lot of time with language arcana. The problem is that the only good, reliable way that I know how to implement one of these functions in terms of the other is with the const_cast/static_cast trick: template <typename T> const T& Vector<T>::operator[] (size_t index) const { /* ... your implementation here ... */ } template <typename T> T& Vector<T>::operator[] (size_t index) { return const_cast<T&>(static_cast<const Vector&>(*this)[index]); } The problem with this setup is that it's extremely tricky to explain and not at all intuitively obvious. When you explain it as "cast to const, then call the const version, then strip off constness" it's a little easier to understand, but the actual syntax is frightening,. Explaining what const_cast is, why it's appropriate here, and why it's almost universally inappropriate elsewhere usually takes me five to ten minutes of lecture time, and making sense of this whole expression often requires more effort than the difference between const T* and T* const. I feel that students need to know about const-overloading and how to do it without needlessly duplicating the code in the two functions, but this trick seems a bit excessive in an introductory C++ programming course. My question is this - is there a simpler way to implement const-overloaded functions in terms of one another? Or is there a simpler way of explaining this existing trick to students? Thanks so much!

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• Preoblem with Precision floating point operation in C

  - by Microkernel

  Hi Guys, For one of my course project I started implementing "Naive Bayesian classifier" in C. My project is to implement a document classifier application (especially Spam) using huge training data. Now I have problem implementing the algorithm because of the limitations in the C's datatype. ( Algorithm I am using is given here, http://en.wikipedia.org/wiki/Bayesian_spam_filtering ) PROBLEM STATEMENT: The algorithm involves taking each word in a document and calculating probability of it being spam word. If p1, p2 p3 .... pn are probabilities of word-1, 2, 3 ... n. The probability of doc being spam or not is calculated using Here, probability value can be very easily around 0.01. So even if I use datatype "double" my calculation will go for a toss. To confirm this I wrote a sample code given below. #define PROBABILITY_OF_UNLIKELY_SPAM_WORD (0.01) #define PROBABILITY_OF_MOSTLY_SPAM_WORD (0.99) int main() { int index; long double numerator = 1.0; long double denom1 = 1.0, denom2 = 1.0; long double doc_spam_prob; /* Simulating FEW unlikely spam words */ for(index = 0; index < 162; index++) { numerator = numerator*(long double)PROBABILITY_OF_UNLIKELY_SPAM_WORD; denom2 = denom2*(long double)PROBABILITY_OF_UNLIKELY_SPAM_WORD; denom1 = denom1*(long double)(1 - PROBABILITY_OF_UNLIKELY_SPAM_WORD); } /* Simulating lot of mostly definite spam words */ for (index = 0; index < 1000; index++) { numerator = numerator*(long double)PROBABILITY_OF_MOSTLY_SPAM_WORD; denom2 = denom2*(long double)PROBABILITY_OF_MOSTLY_SPAM_WORD; denom1 = denom1*(long double)(1- PROBABILITY_OF_MOSTLY_SPAM_WORD); } doc_spam_prob= (numerator/(denom1+denom2)); return 0; } I tried Float, double and even long double datatypes but still same problem. Hence, say in a 100K words document I am analyzing, if just 162 words are having 1% spam probability and remaining 99838 are conspicuously spam words, then still my app will say it as Not Spam doc because of Precision error (as numerator easily goes to ZERO)!!!. This is the first time I am hitting such issue. So how exactly should this problem be tackled?

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• Problem with Precision floating point operation in C

  - by Microkernel

  Hi Guys, For one of my course project I started implementing "Naive Bayesian classifier" in C. My project is to implement a document classifier application (especially Spam) using huge training data. Now I have problem implementing the algorithm because of the limitations in the C's datatype. ( Algorithm I am using is given here, http://en.wikipedia.org/wiki/Bayesian_spam_filtering ) PROBLEM STATEMENT: The algorithm involves taking each word in a document and calculating probability of it being spam word. If p1, p2 p3 .... pn are probabilities of word-1, 2, 3 ... n. The probability of doc being spam or not is calculated using Here, probability value can be very easily around 0.01. So even if I use datatype "double" my calculation will go for a toss. To confirm this I wrote a sample code given below. #define PROBABILITY_OF_UNLIKELY_SPAM_WORD (0.01) #define PROBABILITY_OF_MOSTLY_SPAM_WORD (0.99) int main() { int index; long double numerator = 1.0; long double denom1 = 1.0, denom2 = 1.0; long double doc_spam_prob; /* Simulating FEW unlikely spam words */ for(index = 0; index < 162; index++) { numerator = numerator*(long double)PROBABILITY_OF_UNLIKELY_SPAM_WORD; denom2 = denom2*(long double)PROBABILITY_OF_UNLIKELY_SPAM_WORD; denom1 = denom1*(long double)(1 - PROBABILITY_OF_UNLIKELY_SPAM_WORD); } /* Simulating lot of mostly definite spam words */ for (index = 0; index < 1000; index++) { numerator = numerator*(long double)PROBABILITY_OF_MOSTLY_SPAM_WORD; denom2 = denom2*(long double)PROBABILITY_OF_MOSTLY_SPAM_WORD; denom1 = denom1*(long double)(1- PROBABILITY_OF_MOSTLY_SPAM_WORD); } doc_spam_prob= (numerator/(denom1+denom2)); return 0; } I tried Float, double and even long double datatypes but still same problem. Hence, say in a 100K words document I am analyzing, if just 162 words are having 1% spam probability and remaining 99838 are conspicuously spam words, then still my app will say it as Not Spam doc because of Precision error (as numerator easily goes to ZERO)!!!. This is the first time I am hitting such issue. So how exactly should this problem be tackled?

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• assignment not working in a dll exported C++ class

  - by Jim Jones

  Using VS 2008 Have a C++ class in which I'm calling functions from a 3rd party dll. The definition in the header file is as follows: namespace OITImageExport { class ImageExport { private: SCCERR seResult; /* Error code returned. */ VTHDOC hDoc; /* Input doc handle returned by DAOpenDocument(). */ VTHEXPORT hExport; /* Handle to the export returned by EXOpenExport(). */ VTDWORD dwFIFlags; /* Used in setting the SCCOPT_FIFLAGS option. */ VTCHAR szError[256]; /* Error string buffer. */ VTDWORD dwOutputId; /* Output Format. */ VTDWORD dwSpecType; public: ImageExport(const char* outputId, const char* specType); void ProcessDocument(const char* inputPath, const char* outputPath); ~ImageExport(); }; } In the constructor I initialize two of the class fields having values which come from enumerations in the 3rd party dll: ImageExport::ImageExport(const char* outputId, const char* specType) { if(outputId == "jpeg") { dwOutputId = FI_JPEGFIF; } if(specType == "ansi") { dwSpecType = IOTYPE_ANSIPATH; } seResult = DAInit(); if (seResult != SCCERR_OK) { DAGetErrorString(seResult, szError, sizeof(szError)); fprintf(stderr, "DAInit() failed: %s (0x%04X)\n", szError, seResult); exit(seResult); } } When I use this class inside of a console app, with a main method in another file (all in the same namespace), instantiating the class object and calling the methods, it works like a champ. So, now that I know the basic code works, I open a dll project using the class header and code file. Course I have to add the dll macro, namely: #ifdef IMAGEDLL_EXPORTS #define DLL __declspec(dllexport) #else #define DLL __declspec(dllimport) #endif and changed the class definition to "class DLL ImageExport". Compiled nicely to a dll and .lib file (No errors, No warnings). Now to test this dll I open another console project using the same main method as before and linking to the (dll) lib file. Had problems, which when tracked down were the result of the two fields not being set; both had values of 0. Went back to the first console app and printed out the values: dwOutputId was 1535 (#define FI_JPEGFIF 1535) and dwSpecType was 2 (#define IOTYPE_ANSIPATH 2). Now if I was assigning these values outside of the class, I can see how the visibility could be different, but why is the assignment in the dll not working? Is it something about having a class in the dll?

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• getting html tags from xml and echoing in php?

  - by Whitney Sarah Rogers

  I am trying to echo a result from xml into my html code form expedia. But I ran into a problem. There text is a little messed up: <areaInformation> Distances are calculated in a straight line from the property&apos;s location to the point of interest or attraction, and may not reflect actual travel distance. &lt;br /&gt;&lt;br /&gt; Distances are displayed to the nearest 0.1 mile and kilometre. &lt;p&gt;La Isla Shopping Mall - 0.5 km / 0.3 mi &lt;br /&gt;Yamil Lu&apos;um - 0.5 km / 0.3 mi &lt;br /&gt;Acuario Interactivo - 0.6 km / 0.3 mi &lt;br /&gt;Luxury Avenue - 1.5 km / 0.9 mi &lt;br /&gt;Cancun Golf Club at Pok Ta Pok - 2.2 km / 1.3 mi &lt;br /&gt;Nautilus Diving and Training Center - 2.6 km / 1.6 mi &lt;br /&gt;Cancun Convention Center - 2.8 km / 1.7 mi &lt;br /&gt;Plaza Caracol - 2.8 km / 1.8 mi &lt;br /&gt;Playa Tortuga - 3.1 km / 1.9 mi &lt;br /&gt;Aquaworld - 3.6 km / 2.2 mi &lt;br /&gt;Playa Langosta - 4.1 km / 2.6 mi &lt;br /&gt;Museo de Arte Popular Mexicano - 4.6 km / 2.9 mi &lt;br /&gt;Playa Linda - 5 km / 3.1 mi &lt;br /&gt;Playa Delfines - 6.1 km / 3.8 mi &lt;br /&gt;El Rey Ruins - 6.2 km / 3.8 mi &lt;br /&gt;&lt;/p&gt;&lt;p&gt;The preferred airport for ME Cancun - Complete ME All Inclusive is Cancun, Quintana Roo (CUN-Cancun Intl.) - 14.3 km / 8.9 mi. &lt;/p&gt; </areaInformation> And I echo it in php: <div id="hotelInfo"><?php echo $areaInfo ?></div> And of course I get this in the browser window: Distances are calculated in a straight line from the property's location to the point of interest or attraction, and may not reflect actual travel distance. <br /><br /> Distances are displayed to the nearest 0.1 mile and kilometre. <p>La Isla Shopping Mall - 0.5 km / 0.3 mi <br />Yamil Lu'um - 0.5 km / 0.3 mi <br />Acuario Interac etc. How can I fix this??? Any help would be greatly apreciated! Thanks!

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• exclude private property from print_r or object?

  - by Hailwood

  Basically I am using Code Igniter, and the Code Igniter base class is huge, when I print_r some of my objects they have the base class embedded inside them. this makes it a pain to get the information I actually wanted (the rest of the properties). So, I am wondering if there is a way I can hide, or remove the base class object? I have tried clone $object; unset($object->ci); print_r($object); but of course the ci property is private. the actual function I am using for dumping is: /** * Outputs the given variables with formatting and location. Huge props * out to Phil Sturgeon for this one (http://philsturgeon.co.uk/blog/2010/09/power-dump-php-applications). * To use, pass in any number of variables as arguments. * Optional pass in "true" as final argument to kill script after dump * * @return void */ function dump() { list($callee) = debug_backtrace(); $arguments = func_get_args(); $total_arguments = count($arguments); if (end($arguments) === true) $total_arguments--; echo '<fieldset style="background: #fefefe !important; border:2px red solid; padding:5px">'; echo '<legend style="background:lightgrey; padding:5px;">' . $callee['file'] . ' @ line: ' . $callee['line'] . '</legend><pre>'; $i = 0; foreach ($arguments as $argument) { //if the last argument is true we don't want to display it. if ($i == ($total_arguments) && $argument === true) break; echo '<br/><strong>Debug #' . (++$i) . ' of ' . $total_arguments . '</strong>: '; if ((is_array($argument) || is_object($argument)) && count($argument)) { print_r($argument); } else { var_dump($argument); } } echo '</pre>' . PHP_EOL; echo '</fieldset>' . PHP_EOL; //if the very last argument is "true" then die if (end($arguments) === true) die('Killing Script'); }

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• How to store multiple variables from a File Input of unknown size in Java?

  - by AlphaOmegaStrife

  I'm a total beginner with my first programming assignment in Java. For our programming assignment, we will be given a .txt file of students like so: 3 345 Lisa Miller 890238 Y 2 <-(Number of classes) Mathematics MTH345 4 A Physics PHY357 3 B Bill Wilton 798324 N 2 English ENG378 3 B Philosophy PHL534 3 A Dandy Goat 746333 Y 1 History HIS101 3 A" The teacher will give us a .txt file on the day of turning it in with a list of unknown students. My problem is: I have a specific class for turning the data from the file into variables to be used for a different class in printing it to the screen. However, I do not know of a good way to get the variables from the input file for the course numbers, since that number is not predetermined. The only way I can think of to iterate over that unknown amount is using a loop, but that would just overwrite my variables every time. Also, the teacher has requested that we not use any JCL classes (I don't really know what this means.) Sorry if I have done a poor job of explaining this, but I can't think of a better way to conceptualize it. Let me know if I can clarify. Edit: public static void analyzeData() { Scanner inputStream = null; try { inputStream = new Scanner(new FileInputStream("Programming Assignment 1 Data.txt")); } catch (FileNotFoundException e) { System.out.println("File Programming Assignment 1 Data.txt could not be found or opened."); System.exit(0); } int numberOfStudents = inputStream.nextInt(); int tuitionPerHour = inputStream.nextInt(); String firstName = inputStream.next(); String lastname = inputStream.next(); String isTuitionPaid = inputStream.next(); int numberOfCourses = inputStream.nextInt(); String courseName = inputStream.next(); String courseNumber = inputStream.next(); int creditHours = inputStream.nextInt(); String grade = inputStream.next(); To show the methods I am using now, I am just using a Scanner to read from the file and for Scanner inputStream, I am using nextInt() or next() to get variables from the file. Obviously this will not work when I do not know exactly how many classes each student will have.

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• Twisted + SQLAlchemy and the best way to do it.

  - by Khorkrak

  So I'm writing yet another Twisted based daemon. It'll have an xmlrpc interface as usual so I can easily communicate with it and have other processes interchange data with it as needed. This daemon needs to access a database. We've been using SQL Alchemy in place of hard coding SQL strings for our latest projects - those mostly done for web apps in Pylons. We'd like to do the same for this app and re-use library code that makes use of SQL Alchemy. So what to do? Well of course since that library was written for use in a Pylons app it's all the straight-forward blocking style code that everyone is accustomed to and all of the non-blocking is magically handled by Pylons via threading, thread locals, scoped sessions and so on. So now for Twisted I guess I'm a bit stuck. I could: Just write the sql I need directly if it's minimal and use the dbapi pool in twisted to do runInteractions etc when I need to hit the db. Use the objects and inherently blocking methods in our library and block now and then in my Twisted daemon. Bah. Use sAsync which was last updated in 2008 and kind of reuse the models we have defined already but not really and it does address code that needs to work in Pylons either. Does that even work with the latest version SQL Alchemy? Who knows. That project looked great though - why was it apparently abandoned? Spawn a separate subprocess and have it deal with the library code and all it's blocking, the results being returned back to my daemon when ready as objects marshalled via YAML over xmlrpc. Use deferToThread and then expunge the objects returned having made sure to do eager loads so that I have all my stuff that I might need. Seems kind of ugha to me. I'm also stuck using Python 2.5.4 atm so no 2.6 yet and I don't think I can just do an import from future to get access to the cool new multiprocessing module stuff in there. That's OK though I guess as we've got dealing with interprocess communication down pretty well. So I'm leaning towards option 4 mostly as that would avoid the mortal sin of logic duplication with option 1 while also staying the heck away from threads. Any better ideas?

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• Is it possible to use .data() as a search criteria?

  - by Andrew

  I have a pretty complex chat application going on, and there are multiple chat panes, chat entries, chat submits, etc. going on in the same window. At first I was going to do something like.... <input type="text" class="chattext" id="chattext-42"> <input type="text" class="chattext" id="chattext-93"> <input type="button" class="chatsubmit" id="chatsubmit-42"> <input type="button" class="chatsubmit" id="chatsubmit-93"> ... etc. (of course this is vastly simplified, they'd be in separate divs, separate visibilities, etc) So, when they clicked on a .chatsubmit, it would then get the id of that and find the last two characters for the chat ID. This presents some problems, as it would require rewrites if IDs changed lengths, and seems just plain inelegant to me. I then remembered the .data() facility in jQuery... I thought, maybe I could do it more like this: <input type="text" class="chattext"> ... and add a .data("id", 42) to this one <input type="button" class="chatsubmit"> ... and add a .data("id", 42) So that when they click chatsubmit, it gets the ID, and then finds the chattext with that ID and processes it. But looking at the documentation, I don't see an easy way to search by this. For example, let's say the event target in this case is the chatsubmit with the data('id') of 42... var ID = $(event.target).data('id'); // Sets it to 42 var chattext = ... And here I run into the trouble. How do I find which DOM element matches a class of chattext and a data('id') of 42? Is there any easy method, or do I have to search every .chattext for the one with an id of 42? Or is there another easy way of doing this? I did consider the possibility of the container div having the ID, which would make it, I think,? slightly easier to get. But if this works, it could be dealing with things in other container divs as well, making that not a long-term solution. Edit: Literally seconds after posting this, I found this: http://james.padolsey.com/javascript/extending-jquerys-selector-capabilities/ which includes information on extending the selector to data. So I'll try that out, and in the meantime, is this a completely foolhardy way of handling this?

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• Messing with the stack in assembly and c++

  - by user246100

  I want to do the following: I have a function that is not mine (it really doesn't matter here but just to say that I don't have control over it) and that I want to patch so that it calls a function of mine, preserving the arguments list (jumping is not an option). What I'm trying to do is, to put the stack pointer as it was before that function is called and then call mine (like going back and do again the same thing but with a different function). This doesn't work straight because the stack becomes messed up. I believe that when I do the call it replaces the return address. So, I did a step to preserve the return address saving it in a globally variable and it works but this is not ok because I want it to resist to recursitivy and you know what I mean. Anyway, i'm a newbie in assembly so that's why I'm here. Please, don't tell me about already made software to do this because I want to make things my way. Of course, this code has to be compiler and optimization independent. My code (If it is bigger than what is acceptable please tell me how to post it): // A function that is not mine but to which I have access and want to patch so that it calls a function of mine with its original arguments void real(int a,int b,int c,int d) { } // A function that I want to be called, receiving the original arguments void receiver(int a,int b,int c,int d) { printf("Arguments %d %d %d %d\n",a,b,c,d); } long helper; // A patch to apply in the "real" function and on which I will call "receiver" with the same arguments that "real" received. __declspec( naked ) void patch() { _asm { // This first two instructions save the return address in a global variable // If I don't save and restore, the program won't work correctly. // I want to do this without having to use a global variable mov eax, [ebp+4] mov helper,eax push ebp mov ebp, esp // Make that the stack becomes as it were before the real function was called add esp, 8 // Calls our receiver call receiver mov esp, ebp pop ebp // Restores the return address previously saved mov eax, helper mov [ebp+4],eax ret } } int _tmain(int argc, _TCHAR* argv[]) { FlushInstructionCache(GetCurrentProcess(),&real,5); DWORD oldProtection; VirtualProtect(&real,5,PAGE_EXECUTE_READWRITE,&oldProtection); // Patching the real function to go to my patch ((unsigned char*)real)[0] = 0xE9; *((long*)((long)(real) + sizeof(unsigned char))) = (char*)patch - (char*)real - 5; // calling real function (I'm just calling it with inline assembly because otherwise it seems to works as if it were un patched // that is strange but irrelevant for this _asm { push 666 push 1337 push 69 push 100 call real add esp, 16 } return 0; }

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• Device drivers and Windows

  - by b-gen-jack-o-neill

  Hi, I am trying to complete the picture of how the PC and the OS interacts together. And I am at point, where I am little out of guess when it comes to device drivers. Please, don´t write things like its too complicated, or you don´t need to know when using high programming laguage and winapi functions. I want to know, it´s for study purposes. So, the very basic structure of how OS and PC (by PC I mean of course HW) is how I see it is that all other than direct CPU commands, which can CPU do on itself (arithmetic operation, its registers access and memory access) must pass thru OS. Mainly becouse from ring level 3 you cannot use in and out intructions which are used for acesing other HW. I know that there is MMIO,but it must be set by port comunication first. It was not like this all the time. Even I am bit young to remember MSDOS, I know you could access HW directly, becouse there ws no limitation, no ring mode. So you could to write string to diplay use wheather DOS function, or directly acess video card memory and write it by yourself. But as OS developed, there is no longer this possibility. But it is fine, since OS now handles all the HW comunication, and frankly it more convinient and much more safe (I would say the only option) in multitasking environment. So nowdays you instead of using int instructions to use BIOS mapped function or DOS function you call dll which internally than handles everything you don´t need to know about. I understand this. I also undrstand that device drivers is the piece of code that runs in ring level 0, so it can do all the HW interactions. But what I don´t understand is connection between OS and device driver. Let´s take a example - I want to make a sound card make a sound. So I call windows API to acess sound card, but what happens than? Does windows call device drivers to do so? But if it does call device driver, does it mean, that all device drivers which can be called by winAPI function, must have routines named in some specific way? I mean, when I have new sound card, must its drivers have functions named same as the old one? So Windows can actually call the same function from its perspective? But if Windows have predefined sets of functions requored by device drivers, that it cannot use new drivers that doesent existed before last version of OS came out. Please, help me understand this mess. I am really getting mad. Thanks.

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• Tokenizing a string with variable whitespace

  - by Ron Holcomb

  I've read through a few threads detailing how to tokenize strings, but I'm apparently too thick to adapt their suggestions and solutions into my program. What I'm attempting to do is tokenize each line from a large (5k+) line file into two strings. Here's a sample of the lines: 0 -0.11639404 9.0702948e-05 0.00012207031 0.0001814059 0.051849365 0.00027210884 0.062103271 0.00036281179 0.034423828 0.00045351474 0.035125732 The difference I'm finding between my lines and the other sample input from other threads is that I have a variable amount of whitespace between the parts that I want to tokenize. Anyways, here's my attempt at tokenizing: #include <iostream> #include <iomanip> #include <fstream> #include <string> using namespace std; int main(int argc, char *argv[]) { ifstream input; ofstream output; string temp2; string temp3; input.open(argv[1]); output.open(argv[2]); if (input.is_open()) { while (!input.eof()) { getline(input, temp2, ' '); while (!isspace(temp2[0])) getline(input, temp2, ' '); getline (input, temp3, '\n'); } input.close(); cout << temp2 << endl; cout << temp3 << endl; return 0; } I've clipped it some, since the troublesome bits are here. The issue that I'm having is that temp2 never seems to catch a value. Ideally, it should get populated with the first column of numbers, but it doesn't. Instead, it is blank, and temp3 is populated with the entire line. Unfortunately, in my course we haven't learned about vectors, so I'm not quite sure how to implement them in the other solutions for this I've seen, and I'd like to not just copy-paste code for assignments to get things work without actually understanding it. So, what's the extremely obvious/already been answered/simple solution I'm missing? I'd like to stick to standard libraries that g++ uses if at all possible.

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• C# - periodic data reading and Thread.Sleep()

  - by CaldonCZE

  Hello, my C# application reads data from special USB device. The data are read as so-called "messages", each of them having 24 bytes. The amount of messages that must be read per second may differ (maximal frequency is quite high, about 700 messages per second), but the application must read them all. The only way to read the messages is by calling function "ReadMessage", that returns one message read from the device. The function is from external DLL and I cannot modify it. My solution: I've got a seperate thread, that is running all the time during the program run and it's only job is to read the messages in cycle. The received messages are then processed in main application thread. The function executed in the "reading thread" is the following: private void ReadingThreadFunction() { int cycleCount; try { while (this.keepReceivingMessages) { cycleCount++; TRxMsg receivedMessage; ReadMessage(devHandle, out receivedMessage); //...do something with the message... } } catch { //... catch exception if reading failed... } } This solution works fine and all messages are correctly received. However, the application consumes too much resources, the CPU of my computer runs at more than 80%. Therefore I'd like to reduce it. Thanks to the "cycleCount" variable I know that the "cycling speed" of the thread is about 40 000 cycles per second. This is unnecessarily too much, since I need to receive maximum 700 messagges/sec. (and the device has buffer for about 100 messages, so the cycle speed can be even a little lower) I tried to reduce the cycle speed by suspending the thread for 1 ms by Thread.Sleep(1); command. Of course, this didn't work and the cycle speed became about 70 cycles/second which was not enough to read all messages. I know that this attempt was silly, that putting the thread to sleep and then waking him up takes much longer than 1 ms. However, I don't know what else to do: Is there some other way how to slow the thread execution down (to reduce CPU consumption) other than Thread.Sleep? Or am I completely wrong and should I use something different for this task instead of Thread, maybe Threading.Timer or ThreadPool? Thanks a lot in advance for all suggestions. This is my first question here and I'm a beginner at using threads, so please excuse me if it's not clear enough.

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• Local Variables take 7x longer to access than global variables?

  - by ItzWarty

  I was trying to benchmark the gain/loss of "caching" math.floor, in hopes that I could make calls faster. Here was the test: <html> <head> <script> window.onload = function() { var startTime = new Date().getTime(); var k = 0; for(var i = 0; i < 1000000; i++) k += Math.floor(9.99); var mathFloorTime = new Date().getTime() - startTime; startTime = new Date().getTime(); window.mfloor = Math.floor; k = 0; for(var i = 0; i < 1000000; i++) k += window.mfloor(9.99); var globalFloorTime = new Date().getTime() - startTime; startTime = new Date().getTime(); var mfloor = Math.floor; k = 0; for(var i = 0; i < 1000000; i++) k += mfloor(9.99); var localFloorTime = new Date().getTime() - startTime; document.getElementById("MathResult").innerHTML = mathFloorTime; document.getElementById("globalResult").innerHTML = globalFloorTime; document.getElementById("localResult").innerHTML = localFloorTime; }; </script> </head> <body> Math.floor: <span id="MathResult"></span>ms <br /> var mathfloor: <span id="globalResult"></span>ms <br /> window.mathfloor: <span id="localResult"></span>ms <br /> </body> </html> My results from the test: [Chromium 5.0.308.0]: Math.floor: 49ms var mathfloor: 271ms window.mathfloor: 40ms [IE 8.0.6001.18702] Math.floor: 703ms var mathfloor: 9890ms [LOL!] window.mathfloor: 375ms [Firefox [Minefield] 3.7a4pre] Math.floor: 42ms var mathfloor: 2257ms window.mathfloor: 60ms [Safari 4.0.4[531.21.10] ] Math.floor: 92ms var mathfloor: 289ms window.mathfloor: 90ms [Opera 10.10 build 1893] Math.floor: 500ms var mathfloor: 843ms window.mathfloor: 360ms [Konqueror 4.3.90 [KDE 4.3.90 [KDE 4.4 RC1]]] Math.floor: 453ms var mathfloor: 563ms window.mathfloor: 312ms The variance is random, of course, but for the most part In all cases [this shows time taken]: [takes longer] mathfloor Math.floor window.mathfloor [is faster] Why is this? In my projects i've been using var mfloor = Math.floor, and according to my not-so-amazing benchmarks, my efforts to "optimize" actually slowed down the script by ALOT... Is there any other way to make my code more "efficient"...? I'm at the stage where i basically need to optimize, so no, this isn't "premature optimization"...

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• Javascript problem when setting src for img element in FireFox - string parsing error?

  - by Kevin

  I'm having problems with image's on the page. I'm using Javascript to create the elements, and in FireFox it seems the string that I'm using to set the innerHTML is not being parsed correctly. I'll see this when the server page is requested with invalid GET variables. They look like this (from the PHP script's error handler): GET[] = Array ( [shrink] => true [file_id] => \' file_id \' [refresh] => \' now.getTime() \' ) This only happens for about 5% of requests, which is making it difficult to solve. I have been able to reproduce this myself in FireFox, and Firebug will show that the URL it is trying to fetch is: https://www.domain.com/secure/%27%20+%20image_src%20+%20%27 I read somewhere that it might be related to FireFox prefetching content (can't find it googling now), since it seems to only happen on FireFox. Disabling prefetching in about:config does prevent the problem from occurring, but I'm looking for another solution or workaround that doesn't involve end users changing their configurations. Here's the specifics and code: I have an empty table cell on an HTML page. In JQuery's $(document).ready() function for the page, I used JQuery's $.ajax() method to get some data from the server about what should be in that cell. It returns the file_id variable, which for simplicity I just set below. It then sets the empty table cell to have an image with src that points to a page that will serve the image file depending on what file_id is passed. This part of the code was JQuery originally, so I changed it to straight Javascript but that didn't help anything. //get data about image from server //this is actually done through JQuery's $.ajax() but you get the idea var file_id = 12; //create the src for the img //the refresh is to prevent the image from being cached ever, since the page's //javascript will be it changes //during the course of the page's life var now = new Date(); var image_src = 'serve_image.php?shrink=true&file_id=' + file_id + '&refresh=' + now.getTime(); //create document.getElementById('image_cell').innerHTML = '<A target="_blank" href="serve_image.php?file_id=' + file_id + '">' + '<IMG id=image_element src="' + image_src + '" alt="Loading...">' + '</A>';` Any help would be greatly appreciated. Thanks!

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• Is there a way to efficiently yield every file in a directory containing millions of files?

  - by Josh Smeaton

  I'm aware of os.listdir, but as far as I can gather, that gets all the filenames in a directory into memory, and then returns the list. What I want, is a way to yield a filename, work on it, and then yield the next one, without reading them all into memory. Is there any way to do this? I worry about the case where filenames change, new files are added, and files are deleted using such a method. Some iterators prevent you from modifying the collection during iteration, essentially by taking a snapshot of the state of the collection at the beginning, and comparing that state on each move operation. If there is an iterator capable of yielding filenames from a path, does it raise an error if there are filesystem changes (add, remove, rename files within the iterated directory) which modify the collection? There could potentially be a few cases that could cause the iterator to fail, and it all depends on how the iterator maintains state. Using S.Lotts example: filea.txt fileb.txt filec.txt Iterator yields filea.txt. During processing, filea.txt is renamed to filey.txt and fileb.txt is renamed to filez.txt. When the iterator attempts to get the next file, if it were to use the filename filea.txt to find it's current position in order to find the next file and filea.txt is not there, what would happen? It may not be able to recover it's position in the collection. Similarly, if the iterator were to fetch fileb.txt when yielding filea.txt, it could look up the position of fileb.txt, fail, and produce an error. If the iterator instead was able to somehow maintain an index dir.get_file(0), then maintaining positional state would not be affected, but some files could be missed, as their indexes could be moved to an index 'behind' the iterator. This is all theoretical of course, since there appears to be no built-in (python) way of iterating over the files in a directory. There are some great answers below, however, that solve the problem by using queues and notifications. Edit: The OS of concern is Redhat. My use case is this: Process A is continuously writing files to a storage location. Process B (the one I'm writing), will be iterating over these files, doing some processing based on the filename, and moving the files to another location. Edit: Definition of valid: Adjective 1. Well grounded or justifiable, pertinent. (Sorry S.Lott, I couldn't resist). I've edited the paragraph in question above.

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• Mysterious newInstance method

  - by songsungkyun

  First I show some code. library: axis.jar, dom4j.jar jdk1.5, windowsXP T.java import java.io.StringWriter; import org.apache.axis.utils.StringUtils; import org.dom4j.DocumentHelper; import org.dom4j.io.OutputFormat; import org.dom4j.io.XMLWriter; public class T { public T() { System.out.println("constructor"); } public void test() { System.out.println(StringUtils.unescapeNumericChar("1")); } public String getPrettyXML(String xml) throws Exception { System.out.println("getPrettyXML"); StringWriter sw = new StringWriter(); XMLWriter writer = null; try { OutputFormat format = OutputFormat.createPrettyPrint(); org.dom4j.Document document = DocumentHelper.parseText(xml); writer = new XMLWriter(sw, format); writer.write(document); } catch (Exception e) { throw e; } finally { if (writer != null) { try { writer.close(); } catch (Exception e) { } } } return sw.toString(); } public void a() { System.out.println("a"); } public static void main(String[] args) { new T().test(); } } T2.java public class T2 { public static void main(String[] args) throws Exception { System.out.println("T2"); T t = (T) Class.forName("T").newInstance(); } } Ok, here we go... run as (Of course, I'm run at the directory where T.class, T1.class is) java T2 as you can see, not exist class path. ==console== T2 constructor OK... Now delete throw e line at the catch block on the "getPrettyXML" method of T. Ok, here we go.. run one more time without classpath java T2 You can see below... ==console== T2 Exception in thread "main" java.lang.NoClassDefFoundError: org/dom4j/io/OutputFormat at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Unknown Source) at T2.main(T2.java:5) I know that it's not very important for my life or your life. But it's so mysterisou to me, and my all curiosity. thanks.. ^^

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• jquery animation problem using stop

  - by Flanders

  Hi! When running a Jquery animation like slideDown(), it looks like a number of element-specific css properties is set to be updated at a specific interval and when the animation is complete these properties are unset and the display property is simply set to auto or whatever. At least in firebug you can't see those temporary properties any more. The problem I've encountered is the scenario where we stop the slide down with stop(). The element is then left with the current temporary css values. Which is fine because it has to, but let us say that I stoped the slidedown because I have decided to slide it back up again a bit prematurely. It would look something like this: $(this).slideDown(2000) //The below events is not in queue but will rather start execute almost simultaneously as the above line. (dont remember the exact syntax) $(this).delay(1000).stop().slideUp(2000) The above code might not make much sense, but the point is: After 1 second of sliding down the animation is stopped and it starts to slide back up. Works like a charm. BUT!!! And here is the problem. Once it it has slid back up the elements css properties are reset to the exact values it had 1000ms into the slideDown() animation (when stop() was called). If we now try to run the following: $(this).slideDown(2000) It will slide down to the very point the prior slideDown was aborted and not further at half the speed (since it uses the same time for approximately half the height). This is because the css properties were saved as I see it. But it is not especially wished for. Of course I want it to slide all the way down this time. Due to UI interaction that is hard to predict everything might soon break. The longer animations we use increases the risk of something like this happening. Is this to be considered a bug, or am I doing something wrong? Or maybe it's just a feature that is not supported? I guess I can use a callback function to reset the css properties, but depending on the animation used, different css properties are used to render it, and covering your back would result in quite a not-so-fancy solution.

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• Please Describe Your Struggles with Minimizing Use of Global Variables

  - by MetaHyperBolic

  Most of the programs I write are relatively flowchartable processes, with a defined start and hoped-for end. The problems themselves can be complex but do not readily lean towards central use of objects and event-driven programming. Often, I am simply churning through great varied batches of text data to produce different text data. Only occasionally do I need to create a class: As an example, to track warnings, errors, and debugging message, I created a class (Problems) with one instantiation (myErr), which I believe to be an example of the Singleton design pattern. As a further factor, my colleagues are more old school (procedural) than I and are unacquainted with object-oriented programming, so I am loath to create things they could not puzzle through. And yet I hear, again and again, how even the Singleton design pattern is really an anti-pattern and ought to be avoided because Global Variables Are Bad. Minor functions need few arguments passed to them and have no need to know of configuration (unchanging) or program state (changing) -- I agree. However, the functions in the middle of the chain, which primarily control program flow, have a need for a large number of configuration variables and some program state variables. I believe passing a dozen or more arguments along to a function is a "solution," but hardly an attractive one. I could, of course, cram variables into a single hash/dict/associative array, but that seems like cheating. For instance, connecting to the Active Directory to make a new account, I need such configuration variables as an administrative username, password, a target OU, some default groups, a domain, etc. I would have to pass those arguments down through a variety of functions which would not even use them, merely shuffle them off down through a chain which would eventually lead to the function that actually needs them. I would at least declare the configuration variables to be constant, to protect them, but my language of choice these days (Python) provides no simple manner to do this, though recipes do exist as workarounds. Numerous Stack Overflow questions have hit on the why? of the badness and the requisite shunning, but do not often mention tips on living with this quasi-religious restriction. How have you resolved, or at least made peace with, the issue of global variables and program state? Where have you made compromises? What have your tricks been, aside from shoving around flocks of arguments to functions?

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• Big O Complexity of a method

  - by timeNomad

  I have this method: public static int what(String str, char start, char end) { int count=0; for(int i=0;i<str.length(); i++) { if(str.charAt(i) == start) { for(int j=i+1;j<str.length(); j++) { if(str.charAt(j) == end) count++; } } } return count; } What I need to find is: 1) What is it doing? Answer: counting the total number of end occurrences after EACH (or is it? Not specified in the assignment, point 3 depends on this) start. 2) What is its complexity? Answer: the first loops iterates over the string completely, so it's at least O(n), the second loop executes only if start char is found and even then partially (index at which start was found + 1). Although, big O is all about worst case no? So in the worst case, start is the 1st char & the inner iteration iterates over the string n-1 times, the -1 is a constant so it's n. But, the inner loop won't be executed every outer iteration pass, statistically, but since big O is about worst case, is it correct to say the complexity of it is O(n^2)? Ignoring any constants and the fact that in 99.99% of times the inner loop won't execute every outer loop pass. 3) Rewrite it so that complexity is lower. What I'm not sure of is whether start occurs at most once or more, if once at most, then method can be rewritten using one loop (having a flag indicating whether start has been encountered and from there on incrementing count at each end occurrence), yielding a complexity of O(n). In case though, that start can appear multiple times, which most likely it is, because assignment is of a Java course and I don't think they would make such ambiguity. Solving, in this case, is not possible using one loop... WAIT! Yes it is..! Just have a variable, say, inc to be incremented each time start is encountered & used to increment count each time end is encountered after the 1st start was found: inc = 0, count = 0 if (current char == start) inc++ if (inc > 0 && current char == end) count += inc This would also yield a complexity of O(n)? Because there is only 1 loop. Yes I realize I wrote a lot hehe, but what I also realized is that I understand a lot better by forming my thoughts into words...

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