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  • C/C++: feedback in analyzing a code example

    - by KaiserJohaan
    Hello, I have a piece of code from an assignment I am uncertain about. I feel confident that I know the answer, but I just want to double-check with the community incase there's something I forgot. The title is basically secure coding and the question is just to explain the results. int main() { unsigned int i = 1; unsigned int c = 1; while (i > 0) { i = i*2; c++; } printf("%d\n", c); return 0; } My reasoning is this: At first glance you could imagine the code would run forever, considering it's initialized to a positive value and ever increasing. This of course is wrong because eventually the value will grow so large it will cause an integer overflow. This in turn is not entirely true either, because eventally it will force the variable 'i' to be signed by making the last bit to 1 and therefore regarded as a negative number, therefore terminating the loop. So it is not writing to unallocated memory and therefore cause integer overflow, but rather violating the data type and therefore causing the loop to terminate. I am quite sure this is the reason, but I just want to double check. Any opinions?

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  • help with matlab and Discrete Fourier transform

    - by user504363
    Hi all I have previous experience with Matlab, but the problem that I face some problems in apply a problem in (DSP : Digital signal processing) which is not my study field, but I must finish that problems in days to complete my project. all i want is help me with method and steps of solving this problem in matlab and then I can write the code with myself. the problem is about the signal x(t) = exp(-a*t); 1) what's the Discrete Fourier transform of the sampled signal with sample rate fs 2) if a=1 and fs =1 , plot the amplitude spectrum of sampled signal 3) fix the sampling frequency at fs = 1(hz) [what's it mean ?] and plot the magnitude of the Fourier Transform of the sampled signal at various values of a thanks

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  • Express any number as the sum of 4 prime numbers [Doubts]

    - by WarDoGG
    I was give a problem to express any number as sum of 4 prime numbers. Conditions: Not allowed to use any kind of database. Maximum execution time : 3 seconds Numbers only till 100,000 If the splitting is NOT possible, then return -1 What i did : using the sieve of eratosthenes, i calculated all prime numbers till the specified number. looked up a concept called goldbach conjecture which expresses an even number as the summation of 2 primes. However, i am stuck beyond that. Can anyone help me on this one as to what approach u might take ? The sieve of eratosthenes is taking 2 seconds to count primes till 100,000 :(((

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  • Vector insert() causes program to crash

    - by wrongusername
    This is the first part of a function I have that's causing my program to crash: vector<Student> sortGPA(vector<Student> student) { vector<Student> sorted; Student test = student[0]; cout << "here\n"; sorted.insert(student.begin(), student[0]); cout << "it failed.\n"; ... It crashes right at the sorted part because I can see "here" on the screen but not "it failed." The following error message comes up: Debug Assertion Failed! (a long path here...) Expression: vector emplace iterator outside range For more information on how your program can cause an assertion failure, see the Visual C++ documentation on asserts. I'm not sure what's causing the problem now, since I have a similar line of code elsewhere student.insert(student.begin() + position(temp, student), temp); that does not crash (where position returns an int and temp is another declaration of a struct Student). What can I do to resolve the problem, and how is the first insert different from the second one?

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  • Trying to create an infinite for loop that can stop using function doIt()

    - by JoeOzz
    Hey guys, I'm new to javascript and I'm doing a project for my final in class. I need to make it so this game engine I manipulated causes the generation button to go for an infinite loop. I also need to stop it using (Reset==1). Any help? Here's the code I have so far if that helps: function generation() { for(y2=0; y2<2500; y2++) { tempmapactual[y2]=mapactual[y2]; } for (g=0;g<2500;g++) { neighbours=0; for (h=0;h<8;h++) { if (g+coords[h]>0 && g+coords[h]<2499 && mapactual[g+coords[h]]=="white.gif") {neighbours=neighbours+1;} } if (neighbours>=4 || neighbours==1 || neighbours==0) {tempmapactual[g]="black.gif";} if (neighbours==3) {tempmapactual[g]="white.gif";} } for(y3=0; y3<2500; ++y3) { if (mapactual[y3]!=tempmapactual[y3]) { mapactual[y3]=tempmapactual[y3]; document.images[y3+offset].src=mapactual[y3]; } } } </script> <script> function doIt() { for (i=0; i<X; i++) { // This is where I have trouble. What part of generation() do I call? } if (Reset==1) break; // This will kill the loop instantly. } } </script> <script> window.onload(doIt($(X).value))); </script> <form> <input type="button" value="generate" onClick="generation();"> </form> <form> <input type="text"> </form> <form> <input type="button" value="Infinite Loop!" onclick="doIt();"> </form> <form> <input type="button" value="Reset" onclick="doIt();"> </form>

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  • Java - How to declare table[i][j] elements as instance variables?

    - by JDelage
    All, I am trying to code a Connect4 game. For this, I have created a P4Game class and a P4Board class which represents the i X j dimensions of the Connect4 board. In P4Game, I have the following: public class P4Game{ //INSTANCE VARIABLES private int nbLines; private int nbColumns; private P4Board [][] position; //CONSTRUCTOR public P4Game(int nbLines, int nbColumns){ this.nbColumns = nbColumns; this.nbLines = nbLines; P4Board [][] position = new P4Board [nbLines][nbColumns]; //Creates the table to receive the instances of the P4Board object.*/ for (int i=0; i<nbLines; i++){ for (int j=0; j<nbColumns; j++){ this.position[i][j] = new P4Board(i,j); //Meant to create each object at (line=i, column=j) } } } This causes a NullPointerException in the nested loops where I mention this.position[i][j]. I reference those objects in other methods of this class so I need them to be instance variables. I suppose the exception is due to the fact that I have not listed the table element position[i][j] as an instance variable at the beginning of the class. my question to people here is (1) is my assumption correct, and if so (2) what would be the syntax to declare instance variables of this form? Thank you all for your help with what I realize is a very basic question. Hopefully it will also benefit other newbies. Cheers, JDelage

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  • 47 memory leaks. STL pointers.

    - by icelated
    I have a major amount of memory leaks. I know that the Sets have pointers and i cannot change that! I cannot change anything, but clean up the mess i have... I am creating memory with new in just about every function to add information to the sets. I have a Cd/ DVD/book: super classes of ITEM class and a library class.. In the library class i have 2 functions for cleaning up the sets.. Also, the CD, DVD, book destructors are not being called.. here is my potential leaks.. library.h #pragma once #include <ostream> #include <map> #include <set> #include <string> #include "Item.h" using namespace std; typedef set<Item*> ItemSet; typedef map<string,Item*> ItemMap; typedef map<string,ItemSet*> ItemSetMap; class Library { public: // general functions void addKeywordForItem(const Item* const item, const string& keyword); const ItemSet* itemsForKeyword(const string& keyword) const; void printItem(ostream& out, const Item* const item) const; // book-related functions const Item* addBook(const string& title, const string& author, int const nPages); const ItemSet* booksByAuthor(const string& author) const; const ItemSet* books() const; // music-related functions const Item* addMusicCD(const string& title, const string& band, const int nSongs); void addBandMember(const Item* const musicCD, const string& member); const ItemSet* musicByBand(const string& band) const; const ItemSet* musicByMusician(const string& musician) const; const ItemSet* musicCDs() const; // movie-related functions const Item* addMovieDVD(const string& title, const string& director, const int nScenes); void addCastMember(const Item* const movie, const string& member); const ItemSet* moviesByDirector(const string& director) const; const ItemSet* moviesByActor(const string& actor) const; const ItemSet* movies() const; ~Library(); void Purge(ItemSet &set); void Purge(ItemSetMap &map); }; here is some functions for adding info using new in library. Keep in mind i am cutting out alot of code to keep this post short. library.cpp #include "Library.h" #include "book.h" #include "cd.h" #include "dvd.h" #include <iostream> // general functions ItemSet allBooks; ItemSet allCDS; ItemSet allDVDs; ItemSetMap allBooksByAuthor; ItemSetMap allmoviesByDirector; ItemSetMap allmoviesByActor; ItemSetMap allMusicByBand; ItemSetMap allMusicByMusician; const ItemSet* Library::itemsForKeyword(const string& keyword) const { const StringSet* kw; ItemSet* obj = new ItemSet(); return obj; const Item* Library::addBook(const string& title, const string& author, const int nPages) { ItemSet* obj = new ItemSet(); Book* item = new Book(title,author,nPages); allBooks.insert(item); // add to set of all books obj->insert(item); return item; const Item* Library::addMusicCD(const string& title, const string& band, const int nSongs) { ItemSet* obj = new ItemSet(); CD* item = new CD(title,band,nSongs); return item; void Library::addBandMember(const Item* musicCD, const string& member) { ItemSet* obj = new ItemSet(); (((CD*) musicCD)->addBandMember(member)); obj->insert((CD*) musicCD); here is the library destructor..... Library::~Library() { Purge(allBooks); Purge(allCDS); Purge(allDVDs); Purge(allBooksByAuthor); Purge(allmoviesByDirector); Purge(allmoviesByActor); Purge(allMusicByBand); Purge(allMusicByMusician); } void Library::Purge(ItemSet &set) { for (ItemSet::iterator it = set.begin(); it != set.end(); ++it) delete *it; set.clear(); } void Library::Purge(ItemSetMap &map) { for (ItemSetMap::iterator it = map.begin(); it != map.end(); ++it) delete it->second; map.clear(); } so, basically item, cd, dvd class all have a set like this: typedef set<string> StringSet; class CD : public Item StringSet* music; and i am deleting it like: but those superclasses are not being called.. Item destructor is. CD::~CD() { delete music; } Do, i need a copy constructor? and how do i delete those objects i am creating in the library class? and how can i get the cd,dvd, destructor called? would the addbandmember function located in the library.cpp cause me to have a copy constructor? Any real help you can provide me to help me clean up this mess instead of telling me not to use pointers in my sets i would really appreciate. How can i delete the memory i am creating in those functions? I cannot delete them in the function!!

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  • Read from cin or a file

    - by m42a
    When I try to compile the code istream in; if (argc==1) in=cin; else { ifstream ifn(argv[1]); in=ifn; } gcc fails, complaining that operator= is private. Is there any way to set an istream to different values based on a condition?

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  • Balancing heuristics (for timetable problem)

    - by genesiss
    I'm writing a genetic algorithm for generating timetables. At the moment I'm using these two heuristics: Number of holes between lectures in one day (related) (less holes - bigger score) Each hour has some value, so for each timetable I sum values for hours when lectures are on. (lectures at more appropriate hours - bigger score) I want to balance these two heuristics, so the algorithm wouldn't favor neither one. What would be the best way to achieve this?

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  • Perl : how to interrupt/resume loop by user hitting a key?

    - by Michael Mao
    Hi all: This is for debugging purpose. I've got a for loop that generates some output to Cygwin bash's CLI. I know that I can redirect outputs to text files and use Perl or even just a normal text editor to inspect the values printed out for a particular iteration, just feel that a bit painful. What I am now thinking is, to place a special subroutine inside the for loop, so that it would be "interrupted" at the beginning of each iteration, and Perl script should only resume to run after user/programmer hits a key(the Enter Key from keyboard?) In this way I can directly inspect the values printed out during each iteration. Is there a simple way to do this, without using additional libraries/CPAN ? Many thanks to the hints/suggestions in advance.

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  • Which database I can used and relationship in it ??

    - by mimo-hamad
    My projece make me confused which I didn't find clear things that make me understand the required database and the relationships in it So, would a super one help me to solve it ?!! ;D this is required: 1) Model the data stored in the database (Identify the entities, roles, relationships, constraints, etc.) 2) Write the Oracle commands to create the database, find appropriate data, and populate the database 3) Write five different queries on your database, using the SELECT/FROM/WHERE construct provided in SQL. Your five queries should illustrate several different aspects of database querying, such as: a. Queries over more than one relation (by listing more than one relation in the FROM clause) b. Queries involving aggregate functions, such as SUM, COUNT, and AVG c. Queries involving complicated selects and joins d. Queries involving GROUP BY, HAVING or other similar functions. e. Queries that require the use of the DISTINCT keyword. And this the condition that we need to determine it to solve the required Q's above : 5) It is desired to develop an Internet membership club to buy products at special prices online. To join, new members must be referred by another existing member of the club. The system will keep the following information for each member: The member ID, referring member, birth date, member name, address, phone, mobile, credit card type, number and expiration date. The items are always shipped to the member's address noted in the membership application. The shipping fees will differ for each order.For each item to be requested, the member will select an item from a long list of possible items. For each item in the database, we store an item ID, an item name, description, and list price. The list price will be different from the actual sale price. The available quantity and the back-ordered quantity (the back-ordered quantity is the quantity on-order by the club from its suppliers) is also noted

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  • How could I evaluate this in code?

    - by WM
    There is a medieval puzzle about an old woman and a basket of eggs. On her way to market, a horseman knocks down the old woman and all the eggs are broken. The horseman will pay for the eggs, but the woman does not remember the exact number she had, only that when she took the eggs in pair, there was one left over; similarly, there was one left over when she took them three or five at a time. When she took them seven at a time, however, none were left. Write an application that can determine the smallest number of eggs the woman could have had. It might be a multiple of seven because there are no eggs left when it's seven at a time. But I have a problem. 49 eggs -1=2*24 49 eggs -1=3*16 49 eggs-4=5*9 49 eggs-0=7*7

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  • Why is my code not printing anything to stdout?

    - by WM
    I'm trying to calculate the average of a student's marks: import java.util.Scanner; public class Average { public static void main(String[] args) { int mark; int countTotal = 0; // to count the number of entered marks int avg = 0; // to calculate the total average Scanner Scan = new Scanner(System.in); System.out.print("Enter your average: "); String Name = Scan.next(); while (Scan.hasNextInt()) { mark = Scan.nextInt(); countTotal++; avg = avg + ((mark - avg) / countTotal); } System.out.print( Name + " " + avg ); } }

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  • How to reverse a string?

    - by WM
    Example : hi how are you; output : you are how hi; but wrote this code and im stuck not knowing how to put a string into an array and reverse it..? public class Reverse { public static void main(String[] args) { Scanner text = new Scanner(System.in); System.out.print("Enter your Text : "); String input = text.nextLine(); Scanner text2 = new Scanner(text.nextLine()); String[] array = new String[] ; int i; for(i = 0; i < input.length(); i++) { array[i] = input;

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  • A Simulator for a non-deterministic Push-Down Automaton

    - by shake
    Well, i need to make simulator for non-deterministic Push-Down Automaton. Everything is okey, i know i need to do recursion or something similar. But i do not know how to make that function which would simulate automaton. I got everything else under control, automaton generator, stack ... I am doing it in java, so this is maybe only issue that man can bump on, and i did it. So if anyone have done something similar, i could use advices. This is my current organisation of code: C lasses: class transit: list -contains non deterministic transitions state input sign stack sign class generator it generate automaton from file clas NPA public boolean start() - this function i am having trouble with Of course problem of separate stacks, and input for every branch. I tried to solve it with collection of objects NPA and try to start every object, but it doesn work :((..

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  • Accessing every child class of parent class in Java

    - by darkie15
    Hi All, I have to implement a logic whereby given a child class, I need to access its parent class and all other child class of that parent class, if any. I did not find any API in Java Reflection which allows us to access all child classes of a parent class. Is there any way to do it? Ex. class B extends class A class C extends class A Now using class B, I can find the superclass by calling getSuperClass(). But is there any way to find all the child classes once I have the parent class i.e. class B and class C?? Regards, darkie

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  • Calculate Age, Given Date of Birth

    - by bond
    Given a date of birth, how would I go about calculating an age in C? For example, if today's date is 20/04/2010 and the date of birth given is 12/08/86, then age will be 23 years, 8 months, and 8 days. Any suggestions would be appreciated. Thanks!

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  • File IO, Handling CRLF

    - by aCuria
    Hi, i am writing a program that takes a file and splits it up into multiple small files of a user specified size, then join the multiple small files back again. 1) the code must work for c, c++ 2) i am compiling with multiple compilers. I am reading and writing to the files by using the stl functions fread() and fwrite() The problem I am having pertains to CRLF. If the file I am reading from contains CRLF, then I want to retain it when i split and join the files back together. If the file contains LF, then i want to retain LF. Unfortunately, fread() seems to store CRLF as \n (I think), and whatever is written by fwrite() is compiler-dependent. How do i approach this problem? Thanks.

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  • SQL Query with computed column

    - by plotnick
    help me please with a query. Assume that we have a table with columns: Transaction StartTime EndTime Now, I need a query with computed column of (value = EndTime-Startime). Actually I need to group Users(Transaction has a FK for Users) and sort them by average time spent for transaction.

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  • c program for this quesion

    - by sashi
    suppose that a disk drive has 5000 cylinders, numbered 0 to 4999. the drive is currently serving a request at cylinder 143 and the previous request was at cylinder 125. the ueue of pending requests in the given order is 86,1470,913,17774,948,1509,1022,1750,130. write a 'c' program for finding the total distance in cylinders that the disk arm moves to satisfy all the pending reuests from the current heads position, using SSTF scheduling algorith. seek time is the time for the disk arm to move the head to the cylider containing the desired sector. sstf algorithm selects the minimum seek time from the current head position.

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  • Spatial domain to frequency domain

    - by John Elway
    I know about Fourier Transforms, but I don't know how to apply it here, and I think that is over the top. I gave my ideas of the responses, but I really don't know what I'm looking for... Supposed that you form a low-pass spatial filter h(x,y) that averages all the eight immediate neighbors of a pixel (x,y) but excludes itself. a. Find the equivalent frequency domain filter H(u,v): My answer is to (a): 1/8*H(u-1, v-1) + 1/8*H(u-1, v) + 1/8*H(u-1, v+1) + 1/8*H(u, v-1) + 0 + 1/8*H(u, v+1) + 1/8*H(u+1, v-1) + 1/8*H(u+1, v) + 1/8*H(u-1, v-1) is this the frequency domain? b. Show that your result is again a low-pass filter. does this have to do with the coefficients being positive?

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  • Efective way to avoid integer overflow when multiplying?

    - by Jonathan
    Hi, I'm working on a hash function which gets a string as input. Right now I'm doing a loop and inside the hash (an int variable) is being multiplied by a value and then the ASCII code for the current character is added to the mix. hash = hash * seed + string[i] But sometimes, if the string is big enough there is an integer overflow there, what can I do to avoid it while maintaining the same hash structure? Maybe a bit operation included inside the loop?

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