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  • question about book example - Java Concurrency in Practice, Listing 4.12

    - by mike
    Hi, I am working through an example in Java Concurrency in Practice and am not understanding why a concurrent-safe container is necessary in the following code. I'm not seeing how the container "locations" 's state could be modified after construction; so since it is published through an 'unmodifiableMap' wrapper, it appears to me that an ordinary HashMap would suffice. EG, it is accessed concurrently, but the state of the map is only accessed by readers, no writers. The value fields in the map are syncronized via delegation to the 'SafePoint' class, so while the points are mutable, the keys for the hash, and their associated values (references to SafePoint instances) in the map never change. I think my confusion is based on what precisely the state of the collection is in the problem. Thanks!! -Mike Listing 4.12, Java Concurrency in Practice, (this listing available as .java here, and also in chapter form via google) /////////////begin code @ThreadSafe public class PublishingVehicleTracker { private final Map<String, SafePoint> locations; private final Map<String, SafePoint> unmodifiableMap; public PublishingVehicleTracker( Map<String, SafePoint> locations) { this.locations = new ConcurrentHashMap<String, SafePoint>(locations); this.unmodifiableMap = Collections.unmodifiableMap(this.locations); } public Map<String, SafePoint> getLocations() { return unmodifiableMap; } public SafePoint getLocation(String id) { return locations.get(id); } public void setLocation(String id, int x, int y) { if (!locations.containsKey(id)) throw new IllegalArgumentException( "invalid vehicle name: " + id); locations.get(id).set(x, y); } } // monitor protected helper-class @ThreadSafe public class SafePoint { @GuardedBy("this") private int x, y; private SafePoint(int[] a) { this(a[0], a[1]); } public SafePoint(SafePoint p) { this(p.get()); } public SafePoint(int x, int y) { this.x = x; this.y = y; } public synchronized int[] get() { return new int[] { x, y }; } public synchronized void set(int x, int y) { this.x = x; this.y = y; } } ///////////end code

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  • How to increment counters based on a printed array

    - by Sam Liew
    I managed to developed a simple board of 5x5 using random numbers and array. Big achievement for someone like me! :) Now I have to increment the counters depending on the frequency of the numbers. If the value within 0-49 is printed..then nCounter++ If the value within 50-75 is printed..then pCounter++ something like that. The problem is that I don't know how to increase the counters based on the printed board. Here is the code: #include <stdio.h> #include <stdlib.h> #include <time.h> int main() { //Initialize Variables int randomNumber; int rows; int columns; int hdCounter =0; int hCounter = 0; int cCounter = 0; int pCounter = 0; int nCounter = 0; //Declare board size int board[5][5]; //size of board is 5 x 5 //Create the random number generator seed srand(time(NULL)); //Assign the random numbers from 1 - 25 into variable randomNumber //Create the rows for the board for ( rows = 1; rows <= 5 ; rows++ ) { //Create the colimns for the board for ( columns = 1; columns <= 5 ; columns++ ) { //Assign variable randomNumber into variable board randomNumber = rand() %100 + 1; board[rows][columns] = randomNumber; //print the board printf("%d\t", board[rows][columns]); //calculate the frequency of numbers on the printed board if (randomNumber >= 85 && randomNumber <= 100 ) hdCounter++; else if ( randomNumber >= 75 ) hCounter++; else if ( randomNumber >= 65 ) cCounter++; else if ( randomNumber >= 50 ) pCounter++; else if ( randomNumber >= 1 ) nCounter++; else continue; } //Newline after the end of 5th column. printf("\n\n"); } printf( "N \t P \t C \t H \t HD\n\n" ); printf("%d \t %d \t %d \t %d \t %d \t", nCounter, pCounter, cCounter, hCounter, hdCounter); }//end main I tried replacing randomNumber in the if-statement with board[rows][columns] but I seem to get the same undesired results.

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  • c compilation error

    - by ambika
    hi, this is my error error:static declaration of 'doct' follows non-static declaration error: previous declaration of 'doct' was here. my code int doct(int*); <- here the second error private int doct(int *a) { static int a=0; <- here the first error a++; *a=a; return 0; } give suggestion.

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  • error in C# code

    - by user318068
    hi all . I have a problem with my code in C# . if i click in compiler button , I get the following errors 'System.Collections.Generic.LinkedList' does not contain a definition for 'removeFirst' and no extension method 'removeFirst' accepting a first argument of type 'System.Collections.Generic.LinkedList' could be found (are you missing a using directive or an assembly reference?). and 'System.Collections.Generic.LinkedList' does not contain a definition for 'addLast' and no extension method 'addLast' accepting a first argument of type 'System.Collections.Generic.LinkedList' could be found (are you missing a using directive or an assembly reference?) This is part of a simple program using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Hanoi { public class Sol { public LinkedList<int?> t1 = new LinkedList<int?>(); public LinkedList<int?> t2 =new LinkedList<int?>(); public LinkedList<int?> t3 =new LinkedList<int?>(); public int depth; public LinkedList<Sol> neighbors; public Sol(LinkedList<int?> t1, LinkedList<int?> t2, LinkedList<int?> t3) { this.t1 = t1; this.t2 = t2; this.t3 = t3; neighbors = new LinkedList<Sol>(); } public virtual void getneighbors() { Sol temp = this.copy(); Sol neighbor1 = this.copy(); Sol neighbor2 = this.copy(); Sol neighbor3 = this.copy(); Sol neighbor4 = this.copy(); Sol neighbor5 = this.copy(); Sol neighbor6 = this.copy(); if (temp.t1.Count != 0) { if (neighbor1.t2.Count != 0) { if (neighbor1.t1.First.Value < neighbor1.t2.First.Value) { neighbor1.t2.AddFirst(neighbor1.t1.RemoveFirst()); neighbors.AddLast(neighbor1); } } else { neighbor1.t2.AddFirst(neighbor1.t1.RemoveFirst()); neighbors.AddLast(neighbor1); } if (neighbor2.t3.Count != 0) { if (neighbor2.t1.First.Value < neighbor2.t3.First.Value) { neighbor2.t3.AddFirst(neighbor2.t1.RemoveFirst()); neighbors.AddLast(neighbor2); } } else I hope that you find someone to help me

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  • Problem with pointers

    - by noname
    OK, i have a strange problem. I have this piece of code: int *p; int test; p=&test; In Visual C++ express, in my exsisting project, I get this error: missing type specifier - int assumed. 'p' : 'int' differs in levels of indirection from 'char *' 'initializing' : cannot convert from 'char *' to 'int' But when i create new project, same code is fine. Whats the problem please?

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  • Output character in assembly

    - by lolopolosko
    Please help me! How i can output character that moves around the perimeter of a rectangle (10*5 or 15*7) in console with TASM? .MODEL small .STACK 100h .CODE start: mov ah,03 int 10h mov cx,10 A: push cx mov ah,03 int 10h mov ah,02h inc dl int 10h mov al,42 int 29h pop cx LOOP A mov ah,4ch int 21h end start I do not know how to solve the problem...

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  • Getting segmentation fault after destructor

    - by therealsquiggy
    I'm making a small file reading and data validation program as part of my TAFE (a tertiary college) course, This includes checking and validating dates. I decided that it would be best done with a seperate class, rather than integrating it into my main driver class. The problem is that I'm getting a segmentation fault(core dumped) after my test program runs. Near as I can tell, the error occurs when the program terminates, popping up after the destructor is called. So far I have had no luck finding the cause of this fault, and was hoping that some enlightened soul might show me the error of my ways. date.h #ifndef DATE_H #define DATE_H #include <string> using std::string; #include <sstream> using std::stringstream; #include <cstdlib> using std::exit; #include <iostream> using std::cout; using std::endl; class date { public: explicit date(); ~date(); bool before(string dateIn1, string dateIn2); int yearsBetween(string dateIn1, string dateIn2); bool isValid(string dateIn); bool getDate(int date[], string dateIn); bool isLeapYear(int year); private: int days[]; }; #endif date.cpp #include "date.h" date::date() { days[0] = 31; days[1] = 28; days[2] = 31; days[3] = 30; days[4] = 31; days[5] = 30; days[6] = 31; days[7] = 31; days[8] = 30; days[9] = 31; days[10] = 30; days[11] = 31; } bool date::before(string dateIn1, string dateIn2) { int date1[3]; int date2[3]; getDate(date1, dateIn1); getDate(date2, dateIn2); if (date1[2] < date2[2]) { return true; } else if (date1[1] < date2[1]) { return true; } else if (date1[0] < date2[0]) { return true; } return false; } date::~date() { cout << "this is for testing only, plox delete\n"; } int date::yearsBetween(string dateIn1, string dateIn2) { int date1[3]; int date2[3]; getDate(date1, dateIn1); getDate(date2, dateIn2); int years = date2[2] - date1[2]; if (date1[1] > date2[1]) { years--; } if ((date1[1] == date2[1]) && (date1[0] > date2[1])) { years--; } return years; } bool date::isValid(string dateIn) { int date[3]; if (getDate(date, dateIn)) { if (date[1] <= 12) { int extraDay = 0; if (isLeapYear(date[2])) { extraDay++; } if ((date[0] + extraDay) <= days[date[1] - 1]) { return true; } } } else { return false; } } bool date::getDate(int date[], string dateIn) { string part1, part2, part3; size_t whereIs, lastFound; whereIs = dateIn.find("/"); part1 = dateIn.substr(0, whereIs); lastFound = whereIs + 1; whereIs = dateIn.find("/", lastFound); part2 = dateIn.substr(lastFound, whereIs - lastFound); lastFound = whereIs + 1; part3 = dateIn.substr(lastFound, 4); stringstream p1(part1); stringstream p2(part2); stringstream p3(part3); if (p1 >> date[0]) { if (p2>>date[1]) { return (p3>>date[2]); } else { return false; } return false; } } bool date::isLeapYear(int year) { return ((year % 4) == 0); } and Finally, the test program #include <iostream> using std::cout; using std::endl; #include "date.h" int main() { date d; cout << "1/1/1988 before 3/5/1990 [" << d.before("1/1/1988", "3/5/1990") << "]\n1/1/1988 before 1/1/1970 [" << d.before("a/a/1988", "1/1/1970") <<"]\n"; cout << "years between 1/1/1988 and 1/1/1998 [" << d.yearsBetween("1/1/1988", "1/1/1998") << "]\n"; cout << "is 1/1/1988 valid [" << d.isValid("1/1/1988") << "]\n" << "is 2/13/1988 valid [" << d.isValid("2/13/1988") << "]\n" << "is 32/12/1988 valid [" << d.isValid("32/12/1988") << "]\n"; cout << "blerg\n"; } I've left in some extraneous cout statements, which I've been using to try and locate the error. I thank you in advance.

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  • Problem on a Floyd-Warshall implementation using c++

    - by Henrique
    I've got a assignment for my college, already implemented Dijkstra and Bellman-Ford sucessfully, but i'm on trouble on this one. Everything looks fine, but it's not giving me the correct answer. Here's the code: void FloydWarshall() { //Also assume that n is the number of vertices and edgeCost(i,i) = 0 int path[500][500]; /* A 2-dimensional matrix. At each step in the algorithm, path[i][j] is the shortest path from i to j using intermediate vertices (1..k-1). Each path[i][j] is initialized to edgeCost(i,j) or infinity if there is no edge between i and j. */ for(int i = 0 ; i <= nvertices ; i++) for(int j = 0 ; j <= nvertices ; j++) path[i][j] = INFINITY; for(int j = 0 ; j < narestas ; j++) //narestas = number of edges { path[arestas[j]->v1][arestas[j]->v2] = arestas[j]->peso; //peso = weight of the edge (aresta = edge) path[arestas[j]->v2][arestas[j]->v1] = arestas[j]->peso; } for(int i = 0 ; i <= nvertices ; i++) //path(i, i) = 0 path[i][i] = 0; //test print, it's working fine //printf("\n\n\nResultado FloydWarshall:\n"); //for(int i = 1 ; i <= nvertices ; i++) // printf("distancia ao vertice %d: %d\n", i, path[1][i]); //heres the problem, it messes up, and even a edge who costs 4, and the minimum is 4, it prints 2. //for k = 1 to n for(int k = 1 ; k <= nvertices ; k++) //for i = 1 to n for(int i = 1 ; i <= nvertices ; i++) //for j := 1 to n for(int j = 1 ; j <= nvertices ; j++) if(path[i][j] > path[i][k] + path[k][j]) path[i][j] = path[i][k] + path[k][j]; printf("\n\n\nResultado FloydWarshall:\n"); for(int i = 1 ; i <= nvertices ; i++) printf("distancia ao vertice %d: %d\n", i, path[1][i]); } im using this graph example i've made: 6 7 1 2 4 1 5 1 2 3 1 2 5 2 5 6 3 6 4 6 3 4 2 means we have 6 vertices (1 to 6), and 7 edges (1,2) with weight 4... etc.. If anyone need more info, i'm up to giving it, just tired of looking at this code and not finding an error.

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  • How to map an array to multiple properties using AutoMapper?

    - by Dror Helper
    I need to map a single fixed sized array array to multiple properties. For example given this class: public class Source { public int[] ItemArray{get;set} // always 4 items } I want to map the array to this class public class Dest { public int Item1{get;set;} public int Item1{get;set;} public int Item1{get;set;} public int Item1{get;set;} } Is there a simple way to do it with AutoMapper (without actually mapping each individual field)?

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  • c++ inline functions

    - by user69514
    i'm confused about how to do inline functions in C++.... lets say this function. how would it be turned to an inline function int maximum( int x, int y, int z ) { int max = x; if ( y > max ) max = y; if ( z > max ) max = z; return max; }

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  • Java How to get exact tile location in random tile engine

    - by SYNYST3R1
    I am using the slick2d library. I want to know how to get the exact tile location so when I click on a tile it only changes that tile and not every tile on the screen. My tile generation class public Image[] tiles = new Image[3]; public int width, height; public int[][] index; public Image grass, dirt, selection; boolean selected; int mouseX, mouseY; public void init() throws SlickException { grass = new Image("assets/tiles/grass.png"); dirt = new Image("assets/tiles/dirt.png"); selection = new Image("assets/tiles/selection.png"); tiles[0] = grass; tiles[1] = dirt; width = 50; height = 50; index = new int[width][height]; Random rand = new Random(); for (int x = 0; x < width; x++) { for (int y = 0; y < height; y++) { index[x][y] = rand.nextInt(2); } } } public void update(GameContainer gc) { Input input = gc.getInput(); mouseX = input.getMouseX(); mouseY = input.getMouseY(); if(input.isMouseButtonDown(Input.MOUSE_LEFT_BUTTON)) { selected = true; } else{ selected = false; } } public void render() { for (int x = 0; x < width; x++) { for (int y = 0; y < height; y++) { tiles[index[x][y]].draw(x * 64, y *64); if(IsMouseInsideTile(x, y)) selection.draw(x * 64, y * 64); } } } public boolean IsMouseInsideTile(int x, int y) { return (mouseX >= x * 64 && mouseX <= (x + 1) * 64 && mouseY >= y * 64 && mouseY <= (y + 1) * 64); } I have tried a couple different ways to change the tile I am clicking on, but I don't understand how to do it.

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  • Pointers to class fields

    - by newbie_cpp
    My task is as follows : Using pointers to class fields, create menu allowing selection of ice, that Person can buy in Ice shop. Buyer will be charged with waffel and ice costs. Selection of ice and charging buyers account must be shown in program. Here's my Person class : #include <iostream> using namespace std; class Iceshop { const double waffel_price = 1; public: } class Person { static int NUMBER; char* name; int age; const int number; double plus, minus; public: class Account { int number; double resources; public: Account(int number, double resources) : number(number), resources(resources) {} } Person(const char* n, int age) : name(strcpy(new char[strlen(n)+1],n)), number(++NUMBER), plus(0), minus(0), age(age) {} Person::~Person(){ cout << "Destroying resources" << endl; delete [] name; } friend void show(Person &p); int* take_age(){ return &age; } char* take_name(){ return name; } void init(char* n, int a) { name = n; age = a; } Person& remittance(double d) { plus += d; return *this; } Person& paycheck(double d) { minus += d; return *this; } Account* getAccount(); }; int Person:: Person::Account* Person::getAccount() { return new Account(number, plus - minus); } void Person::Account::remittance(double d){ resources = resources + d; } void Person::Account::paycheck(double d){ resources = resources - d; } void show(Person *p){ cout << "Name: " << p->take_name() << "," << "age: " << p->take_age() << endl; } int main(void) { Person *p = new Person; p->init("Mary", 25); show(p); p->remittance(100); system("PAUSE"); return 0; } How to start this task ? Where and in what form should I store menu options ?

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  • C++/CLI HTTP Proxy problems...

    - by darkantimatter
    Hi, I'm trying(very hard) to make a small HTTP Proxy server which I can use to save all communications to a file. Seeing as I dont really have any experience in the area, I used a class from codeproject.com and some associated code to get started (It was made in the old CLI syntax, so I converted it). I couldn't get it working, so I added lots more code to make it work (threads etc), and now it sort of works. Basically, it recieves something from a client (I just configured Mozilla Firefox to route its connections through this proxy) and then routes it to google.com. After it sends Mozilla's data to google, recieves a responce, and sends that to Mozilla. This works fine, but then the proxy fails to recieve any data from Mozilla. It just loops in the Sleep(50) section. Anyway, heres the code: ProxyTest.cpp: #include "stdafx.h" #include "windows.h" #include "CHTTPProxy.h" public ref class ClientThread { public: System::Net::Sockets::TcpClient ^ pClient; CHttpProxy ^ pProxy; System::Int32 ^ pRecieveBufferSize; System::Threading::Thread ^ Thread; ClientThread(System::Net::Sockets::TcpClient ^ sClient, CHttpProxy ^ sProxy, System::Int32 ^ sRecieveBufferSize) { pClient = sClient; pProxy = sProxy; pRecieveBufferSize = sRecieveBufferSize; }; void StartReading() { Thread = gcnew System::Threading::Thread(gcnew System::Threading::ThreadStart(this,&ClientThread::ThreadEntryPoint)); Thread->Start(); }; void ThreadEntryPoint() { char * bytess; bytess = new char[(int)pRecieveBufferSize]; memset(bytess, 0, (int)pRecieveBufferSize); array<unsigned char> ^ bytes = gcnew array<unsigned char>((int)pRecieveBufferSize); array<unsigned char> ^ sendbytes; do { if (pClient->GetStream()->DataAvailable) { try { do { Sleep(100); //Lets wait for whole packet to get cached (If it even does...) unsigned int k = pClient->GetStream()->Read(bytes, 0, (int)pRecieveBufferSize); //Read it for(unsigned int i=0; i<(int)pRecieveBufferSize; i++) bytess[i] = bytes[i]; Console::WriteLine("Packet Received:\n"+gcnew System::String(bytess)); pProxy->SendToServer(bytes,pClient->GetStream()); //Now send it to google! pClient->GetStream()->Flush(); } while(pClient->GetStream()->DataAvailable); } catch (Exception ^ e) { break; } } else { Sleep(50); //It just loops here because it thinks mozilla isnt sending anything if (!(pClient->Connected)) break; }; } while (pClient->GetStream()->CanRead); delete [] bytess; pClient->Close(); }; }; int main(array<System::String ^> ^args) { System::Collections::Generic::Stack<ClientThread ^> ^ Clients = gcnew System::Collections::Generic::Stack<ClientThread ^>(); System::Net::Sockets::TcpListener ^ pTcpListener = gcnew System::Net::Sockets::TcpListener(8080); pTcpListener->Start(); System::Net::Sockets::TcpClient ^ pTcpClient; while (1) { pTcpClient = pTcpListener->AcceptTcpClient(); //Wait for client ClientThread ^ Client = gcnew ClientThread(pTcpClient, gcnew CHttpProxy("www.google.com.au", 80), pTcpClient->ReceiveBufferSize); //Make a new object for this client Client->StartReading(); //Start the thread Clients->Push(Client); //Add it to the list }; pTcpListener->Stop(); return 0; } CHTTPProxy.h, from http://www.codeproject.com/KB/IP/howtoproxy.aspx with a lot of modifications: //THIS FILE IS FROM http://www.codeproject.com/KB/IP/howtoproxy.aspx. I DID NOT MAKE THIS! BUT I HAVE MADE SEVERAL MODIFICATIONS! #using <mscorlib.dll> #using <SYSTEM.DLL> using namespace System; using System::Net::Sockets::TcpClient; using System::String; using System::Exception; using System::Net::Sockets::NetworkStream; #include <stdio.h> ref class CHttpProxy { public: CHttpProxy(System::String ^ szHost, int port); System::String ^ m_host; int m_port; void SendToServer(array<unsigned char> ^ Packet, System::Net::Sockets::NetworkStream ^ sendstr); }; CHttpProxy::CHttpProxy(System::String ^ szHost, int port) { m_host = gcnew System::String(szHost); m_port = port; } void CHttpProxy::SendToServer(array<unsigned char> ^ Packet, System::Net::Sockets::NetworkStream ^ sendstr) { TcpClient ^ tcpclnt = gcnew TcpClient(); try { tcpclnt->Connect(m_host,m_port); } catch (Exception ^ e ) { Console::WriteLine(e->ToString()); return; } // Send it if ( tcpclnt ) { NetworkStream ^ networkStream; networkStream = tcpclnt->GetStream(); int size = Packet->Length; networkStream->Write(Packet, 0, size); array<unsigned char> ^ bytes = gcnew array<unsigned char>(tcpclnt->ReceiveBufferSize); char * bytess = new char[tcpclnt->ReceiveBufferSize]; Sleep(500); //Wait for responce do { unsigned int k = networkStream->Read(bytes, 0, (int)tcpclnt->ReceiveBufferSize); //Read from google for(unsigned int i=0; i<k; i++) { bytess[i] = bytes[i]; if (bytess[i] == 0) bytess[i] = ' '; //Dont terminate the string if (bytess[i] < 8) bytess[i] = ' '; //Somethings making the computer beep, and its not 7?!?! }; Console::WriteLine("\n\nAbove packet sent to google. Google Packet Received:\n"+gcnew System::String(bytess)); sendstr->Write(bytes,0,k); //Send it to mozilla Console::WriteLine("\n\nAbove packet sent to client..."); //Sleep(1000); } while(networkStream->DataAvailable); delete [] bytess; } return; } Any help would be much appreciated, I've tried for hours.

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  • initializing a vector of custom class in c++

    - by Flamewires
    Hey basically Im trying to store a "solution" and create a vector of these. The problem I'm having is with initialization. Heres my class for reference class Solution { private: // boost::thread m_Thread; int itt_found; int dim; pfn_fitness f; double value; std::vector<double> x; public: Solution(size_t size, int funcNo) : itt_found(0), x(size, 0.0), value(0.0), dim(30), f(Eval_Functions[funcNo]) { for (int i = 1; i < (int) size; i++) { x[i] = ((double)rand()/((double)RAND_MAX))*maxs[funcNo]; } } Solution() : itt_found(0), x(31, 0.0), value(0.0), dim(30), f(Eval_Functions[1]) { for (int i = 1; i < 31; i++) { x[i] = ((double)rand()/((double)RAND_MAX))*maxs[1]; } } Solution operator= (Solution S) { x = S.GetX(); itt_found = S.GetIttFound(); dim = S.GetDim(); f = S.GetFunc(); value = S.GetValue(); return *this; } void start() { value = f (dim, x); } /* plus additional getter/setter methods*/ } Solution S(30, 1) or Solution(2, 5) work and initalizes everything, but I need X of these solution objects. std::vector<Solution> Parents(X) will create X solutions with the default constructor and i want to construct using the (int, int) constructor. Is there any easy(one liner?) way to do this? Or would i have to do something like: size_t numparents = 10; vector<Solution> Parents; Parents.reserve(numparents); for (int i = 0; i<(int)numparents; i++) { Solution S(31, 0); Parents.push_back(S); }

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  • Import? Initialize? what do to?

    - by Jeremy B
    I'm working on homework and I'm close but I am having an issue. I just learned how to work with packages in eclipse so I have a class that is importing another class from a package (I think I said that right) The main prompts the user to enter an integer between -100 and 100 and I am having an issue with validating it. I know the issue is where I'm importing I'm just unsure the direction I need to go to fix it. This is a section of my main code. (my issue starts with the last couple lines if you want to skip ahead) import myUtils.util.Console; public class ConsoleTestApp { public static void main(String args[]) { // create the Console object Console c = new Console(); // display a welcome message c.println("Welcome to the Console Tester application"); c.println(); // int c.println("Int Test"); int i = c.getIntWithinRange("Enter an integer between -100 and 100: ", -101, 101); c.println(); I have a class called Console that is located in another package that I believe I have properly imported. here is the code I am stuck on in my console class. public int getIntWithinRange(String prompt, int min, int max) { int i = 0; boolean isValid = false; while (isValid == false) { System.out.println(prompt); if (sc.hasNextInt()) { //if user chooses menu option less than 1 the program will print an error message i = sc.nextInt(); if (i < min) { System.out.println("Error! Please enter an int greater than -100"); } else if (i > max) { System.out.println("Error! Please enter an int less than 100"); } else isValid = true; } else System.out.println("Error! Invalid number value"); sc.nextLine(); } // return the int return i; } when I run this I keep getting my last print which is an invalid number value. am I not importing the code from the main method in the other console properly?

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  • Why is a c++ reference considered safer than a pointer?

    - by anand.arumug
    When the c++ compiler generates very similar assembler code for a reference and pointer, why is using references preferred (and considered safer) compared to pointers? I did see Difference between pointer variable and reference variable in C++ which discusses the differences between them. EDIT-1: I was looking at the assembler code generated by g++ for this small program: int main(int argc, char* argv[]) { int a; int &ra = a; int *pa = &a; }

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  • Linked lists in Java - help with assignment

    - by user368241
    Representation of a string in linked lists In every intersection in the list there will be 3 fields : The letter itself. The number of times it appears consecutively. A pointer to the next intersection in the list. The following class CharNode represents a intersection in the list : public class CharNode { private char _data; private int _value; private charNode _next; public CharNode (char c, int val, charNode n) { _data = c; _value = val; _next = n; } public charNode getNext() { return _next; } public void setNext (charNode node) { _next = node; } public int getValue() { return _value; } public void setValue (int v) { value = v; } public char getData() { return _data; } public void setData (char c) { _data = c; } } The class StringList represents the whole list : public class StringList { private charNode _head; public StringList() { _head = null; } public StringList (CharNode node) { _head = node; } } Add methods to the class StringList according to the details : (I will add methods gradually according to my specific questions) (Pay attention, these are methods from the class String and we want to fulfill them by the representation of a string by a list as explained above) public int indexOf (int ch) - returns the index in the string it is operated on of the first appeareance of the char "ch". If the char "ch" doesn't appear in the string, returns -1. If the value of fromIndex isn't in the range, returns -1. Pay attention to all the possible error cases. Write what is the time complexity and space complexity of every method that you wrote. Make sure the methods you wrote are effective. It is NOT allowed to use ready classes of Java. It is NOT allowed to move to string and use string operations. Here is my try to write the method indexOf (int ch). Kindly assist me with fixing the bugs so I can move on. public int indexOf (int ch) { int count = 0; charNode pose = _head; if (pose == null ) { return -1; } for (pose = _head; pose!=null && pose.getNext()!='ch'; pose = pose.getNext()) { count++; } if (pose!=null) return count; else return -1; }

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  • "Use of uninitialised value" despite of memset

    - by Framester
    Hi there, I allocate a 2d array and use memset to fill it with zeros. #include<stdio.h> #include<string.h> #include<stdlib.h> void main() { int m=10; int n =10; int **array_2d; array_2d = (int**) malloc(m*sizeof(int*)); if(array_2d==NULL) { printf("\n Could not malloc 2d array \n"); exit(1); } for(int i=0;i<m;i++) { ((array_2d)[i])=malloc(n*sizeof(int)); memset(((array_2d)[i]),0,sizeof(n*sizeof(int))); } for(int i=0; i<10;i++){ for(int j=0; j<10;j++){ printf("(%i,%i)=",i,j); fflush(stdout); printf("%i ", array_2d[i][j]); } printf("\n"); } } Afterwards I use valgrind [1] to check for memory errors. I get following error: Conditional jump or move depends on uninitialised value(s) for line 24 (printf("%i ", array_2d[i][j]);). I always thought memset is the function to initialize arrays. How can I get rid off this error? Thanks! Valgrind output: ==3485== Memcheck, a memory error detector ==3485== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al. ==3485== Using Valgrind-3.5.0-Debian and LibVEX; rerun with -h for copyright info ==3485== Command: ./a.out ==3485== (0,0)=0 (0,1)===3485== Use of uninitialised value of size 4 ==3485== at 0x409E186: _itoa_word (_itoa.c:195) ==3485== by 0x40A1AD1: vfprintf (vfprintf.c:1613) ==3485== by 0x40A8FFF: printf (printf.c:35) ==3485== by 0x8048724: main (playing_with_valgrind.c:39) ==3485== ==3485== ==3485== ---- Attach to debugger ? --- [Return/N/n/Y/y/C/c] ---- ==3485== Conditional jump or move depends on uninitialised value(s) ==3485== at 0x409E18E: _itoa_word (_itoa.c:195) ==3485== by 0x40A1AD1: vfprintf (vfprintf.c:1613) ==3485== by 0x40A8FFF: printf (printf.c:35) ==3485== by 0x8048724: main (playing_with_valgrind.c:39) [1] valgrind --tool=memcheck --leak-check=yes --show-reachable=yes --num-callers=20 --track-fds=yes --db-attach=yes ./a.out [gcc-cmd] gcc -std=c99 -lm -Wall -g3 playing_with_valgrind.c

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  • creating an array of objects in c++

    - by tim22
    I'm trying to create an array of objects in c++. I'm creating a employee object, from my constructor in my company class here: employee obj(int tempIdNum, double tempBase, double tempSales, double tempRate); emp[tempcount]=obj; (this doesn't work?) Emp is the name of the array which is defined here, located in my company h file. Employee emp[4]; more code: Company::Company(string name, string fileName){ string str; int tempcount; int tempIdnum; double tempBase; double tempSales; double tempRate; double num; double arr[16]; this->name=name; //Commission temp; ifstream readFile; readFile.open("fileName"); int inc=0; while(tempcount<4){ for(int i=0+inc; i<4+inc; i++){ readFile>>num; arr[i-inc]=num; } tempIdnum=(int)(arr[0]); tempBase=arr[1]; tempSales=arr[2]; tempRate=arr[3]; Employee obj(int tempIdNum, double tempBase, double tempSales, double tempRate); emp[tempcount]=obj; inc+=4; tempcount++; } readFile.close(); } Here is some more from my h file #include <string> include "Commission.h" using namespace std; ifndef Company_H define Company_H class Company{ private: string name; //name of company Employee emp[4]; //array of payrool info about 4 commission employees int numEmp; //number of employees public: Company(); Company(string name, string fileName); ~Company(); string getName(); Commission getEmployee(int element); int getNumEmp(); }; endif enter code here Does not compile: 46 E:\exercise2\Company.cpp no match for 'operator=' in '((Company*)this)-Company::emp[tempcount] = obj'

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  • C newbie malloc question

    - by roufamatic
    Why doesn't this print 5? void writeValue(int* value) { value = malloc(sizeof(int)); *value = 5; } int main(int argc, char * argv) { int* value = NULL; writeValue(value); printf("value = %d\n", *value); // error trying to access 0x00000000 } and how can I modify this so it would work while still using a pointer as an argument to writeValue?

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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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  • Setting last N bits in an array

    - by Martin
    I'm sure this is fairly simple, however I have a major mental block on it, so I need a little help here! I have an array of 5 integers, the array is already filled with some data. I want to set the last N bits of the array to be random noise. [int][int][int][int][int] set last 40 bits [unchanged][unchanged][unchanged][24 bits of old data followed 8 bits of randomness][all random] This is largely language agnostic, but I'm working in C# so bonus points for answers in C#

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