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  • Why I have to redeclare a virtual function while overriding [C++]

    - by Neeraj
    #include <iostream> using namespace std; class Duck { public: virtual void quack() = 0; }; class BigDuck : public Duck { public: // void quack(); (uncommenting will make it compile) }; void BigDuck::quack(){ cout << "BigDuckDuck::Quack\n"; } int main() { BigDuck b; Duck *d = &b; d->quack(); } Consider this code, the code doesn't compiles. However when I declare the virtual function in the subclass, then it compiles fine. The compiler already has the signature of the function which the subclass will override, then why a redeclaration is required? Any insights.

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  • 'array bound is not an integer constant' when defining size of array in class, using an element of a const array

    - by user574733
    #ifndef QWERT_H #define QWERT_H const int x [] = {1, 2,}; const int z = 3; #endif #include <iostream> #include "qwert.h" class Class { int y [x[0]]; //error:array bound is not an integer constant int g [z]; //no problem }; int main () { int y [x[0]]; //no problem Class a_class; } I can't figure out why this doesn't work. Other people with this problem seem to be trying to dynamically allocate arrays. Any help is much appreciated.

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  • can we write this in C++ switch ?

    - by jellly
    #include <iostream> using namespace std; int main(){ char i; cin >>i; switch (i){ case ('e'||'i'||'o'||'u'||'a'): cout<<"Vowel"; break; case ('+'||'-'||'/'||'*'||'%'): cout<<"Op"; break; } return 0; } if not than how can we use comparison or logical operators in switch ? & why cant we declare and initialize variable in single case without using scope ?

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  • Unit testing a functions whose purposes is side effects

    - by David
    How would you unit test do_int_to_string_conversion? #include <string> #include <iostream> void do_int_to_string_conversion(int i, std::string& s) { switch(i) { case 1: s="1"; break; case 2: s="2"; break; default: s ="Nix"; } std::cout << s << "\n"; } int main(int argc, char** argv){ std::string little_s; do_int_to_string_conversion(1, little_s); do_int_to_string_conversion(2, little_s); do_int_to_string_conversion(3, little_s); }

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  • class classname(value); & class classname=value; difference when constructor is explicit

    - by Mahesh
    When constructor is explicit, it isn't used for implicit conversions. In the given snippet, constructor is marked as explicit. Then why in case foo obj1(10.25); it is working and in foo obj2=10.25; it isn't working ? #include <iostream> class foo { int x; public: explicit foo( int x ):x(x) {} }; int main() { foo obj(10.25); // Not an error. Why ? foo obj2 = 10.25; // Error getchar(); return 0; } error: error C2440: 'initializing' : cannot convert from 'double' to 'foo'

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  • How to make a rectangle on screen invisible to screen capture ?

    - by Kesarion
    How can I create a rectangle on the screen that is invisible to any sort of screen capture(printscreen or aplications) ? By create a rectangle on screen I mean something like this: #include <Windows.h> #include <iostream> void drawRect(){ HDC screenDC = ::GetDC(0); ::Rectangle(screenDC, 200, 200, 300, 300); ::ReleaseDC(0, screenDC); } int main(void){ char c; std::cin >> c; if (c == 'd') drawRect(); std::cin >> c; return 0; } I'm using Visual Studio 2010 on Windows XP

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  • How To Parse String File Txt Into Array With C++

    - by Ibnu Syuhada
    I am trying to write a C++ program, but I am not familiar with C++. I have a .txt file, which contains values as follows: 0 0.0146484 0.0292969 0.0439453 0.0585938 0.0732422 0.0878906 What I have done in my C++ code is as follows: #include <iostream> #include <fstream> using namespace std; int main() { string line; ifstream myReadFile; myReadFile.open("Qi.txt"); if(myReadFile.is_open()) { while(myReadFile.good()) { getline(myReadFile,line); cout << line << endl; } myReadFile.close(); } return 0; } I would like to make the output of the program an array, i.e. line[0] = 0 line[1] = 0.0146484 line[2] = 0.0292969 line[3] = 0.0439453 line[4] = 0.0585938 line[5] = 0.0732422 line[6] = 0.0878906

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  • Why the streams in C++?

    - by oh boy
    As you all know there are libraries using streams such as iostream and fstream. My question is: Why streams? Why didn't they stick with functions similar to print, fgets and so on (for example)? They require their own operators << and >> but all they do could be implemented in simple functions like above, also the function printf("Hello World!"); is a lot more readable and logical to me than cout << "Hello World"; I also think that all of those string abstractions in C++ all compile down to (less efficient) standard function calls in binary.

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  • what is the reason i am getting out put is 111?

    - by kam
    Hi, #include "stdafx.h" #include<iostream.h> template<class T> class Sample { public: Sample(); static int i; }; template<class T> int Sample<T>::i = 0; template<class T> Sample<T>::Sample() { i++; cout<<i; } void main() { Sample<int>s1; Sample<float>s2; Sample<char>s3; } output: 111 what is the reason i am getting out put is 111?

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  • C++ Char without Limit

    - by Lienau
    I'm pretty well versed in C#, but I decided it would be a good idea to learn C++ as well. The only thing I can't figure out is chars. I know you can use the string lib but I also want to figure out chars. I know you can set a char with a limit like this: #include <iostream> using namespace std; int main() { char c[128] = "limited to 128"; cout << c << endl; system("pause"); return 0; } But how would I make a char without a limit? I've seen chars with * but I though that was for pointers. Any help is greatly appreciated.

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  • Switch/Case statements in C++

    - by vgoklani
    Regarding the switch/case statement in the C++ code below: "Case 1" is obviously false, so how/why does it enter the do-while loop? #include <iostream> using namespace std; int main() { int test = 4; switch(test) { case 1: do { case 2: test++; case 3: test++; case 4: cout << "How did I get inside the do-while loop?" << endl; break; case 5: test++; } while(test > 0); cout << test << endl; } }

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  • Shuffle array variables in a pre-specified order, without using extra memory of "size of input array"

    - by Eternal Learner
    Input : A[4] = {0,4,-1,1000} - Actual Array P[4] = {1,0,3,2} - Order to be reshuffled Output: A[4] = {4,0,1000,-1} Condition : Don't use an additional array as memory. Can use an extra variable or two. Problem : I have the below program in C++, but this fails for certain inputs of array P. #include<iostream> using namespace std; void swap(int *a_r,int *r) { int temp = *r; *r = *a_r; *a_r = temp; } int main() { int A[4] = {0,4,-1,1000}; int P[4] = {3,0,1,2}; int value = A[0] , dest = P[0]; for(int i=0; i<4;i++) { swap(&A[dest],&value); dest = P[dest]; } for(int i=0;i<4;i++) cout<<A[i]<<" "; }

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  • Feedback + Bad output

    - by user1770094
    So I've got an assignment I think I'm more or less done with, but there is something which is messing up the output badly somewhere down the line, or even the calculation, and I don't see where the problem is. The assignment is to make a game in which a certain ammount of players run up through a tunnel towards a spot,where they will stop and spin around it,and then their dizziness is supposed to make them randomly either progress towards goal or regress back towards start.And each time they get another spot closer to goal,they get another "marking",and it goes on like this until one of them reaches goal. The program includes three files: one main.cpp,one header file and another cpp file. The header file: #ifndef COMPETITOR_H #define COMPETITOR_H #include <string> using namespace std; class Competitor { public: void setName(); string getName(); void spin(); void move(); int checkScore(); void printResult(); private: string name; int direction; int markedSpots; }; #endif // COMPETITOR_H The second cpp file: #include <iostream> #include <string> #include <cstdlib> #include <ctime> #include "Competitor.h" using namespace std; void Competitor::setName() { cin>>name; } string Competitor::getName() { return name; } void Competitor::spin() { srand(time(NULL)); direction = rand()%1+0; } void Competitor::move() { if(direction == 1) { markedSpots++; } else if(direction == 0 && markedSpots != 0) { markedSpots--; } } int Competitor::checkScore() { return markedSpots; } void Competitor::printResult() { if(direction == 1) { cout<<" is heading towards goal and has currently "<<markedSpots<<" markings."; } else if(direction == 0) { cout<<"\n"<<getName()<<" is heading towards start and has currently "<<markedSpots<<" markings."; } } The main cpp file: #include <iostream> #include <string> #include <cstdlib> #include <ctime> #include "Competitor.h" using namespace std; void inputAndSetNames(Competitor comps[],int nrOfComps); void makeTwist(Competitor comps[],int nrOfComps); void makeMove(Competitor comps[],int nrOfComps); void showAll(Competitor comps[],int nrOfComps); int winner(Competitor comps[],int nrOfComps, int nrOfTwistPlaces); int main() { int nrOfTwistPlaces; int nrOfComps; int noWinner = -1; int laps = 0; cout<<"How many spinning places should there be? "; cin>>nrOfTwistPlaces; cout<<"How many competitors should there be? "; cin>>nrOfComps; Competitor * comps = new Competitor[nrOfComps]; inputAndSetNames(comps, nrOfComps); do { laps++; cout<<"\nSpin "<<laps<<":"; makeTwist(comps, nrOfComps); makeMove(comps, nrOfComps); showAll(comps, nrOfComps); }while(noWinner == -1); delete [] comps; return 0; } void inputAndSetNames(Competitor comps[],int nrOfComps) { cout<<"Type in the names of the "<<nrOfComps<<" competitors:\n"; for(int i=0;i<nrOfComps;i++) { comps[i].setName(); } cout<<"\n"; } void makeTwist(Competitor comps[],int nrOfComps) { for(int i=0;i<nrOfComps;i++) { comps[i].spin(); } } void makeMove(Competitor comps[],int nrOfComps) { for(int i=0;i<nrOfComps;i++) { comps[i].move(); } } void showAll(Competitor comps[],int nrOfComps) { for(int i=0;i<nrOfComps;i++) { comps[i].printResult(); } cout<<"\n\n"; system("pause"); } int winner(Competitor comps[],int nrOfComps, int nrOfTwistPlaces) { int end = 0; int score = 0; for(int i=0;i<nrOfComps;i++) { score = comps[i].checkScore(); if(score == nrOfTwistPlaces) { end = 1; } else end = -1; } return end; } I'd be grateful if you would point out other mistakes if you see any.Thanks in advance.

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  • trying to sort a simple string in c++

    - by every_answer_gets_a_point
    #include "stdio.h" #include "conio.h" #include <iostream> using namespace std; int main (void) { char my_char[] = "happy birthday"; int i; bool j=false; char my_char_temp[1]; do { for (i=0;i<sizeof(my_char)-2;i++) { j=false; if (my_char[i+1] < my_char[i]) { my_char_temp[0]=my_char[i+1]; my_char[i+1] = my_char[i]; my_char[i] = my_char_temp[0]; j=true; } } }while (j); cout << my_char; } what am i doing wrong? im just trying to sort the letters within the char the output i get is completely wrong

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  • Misunderstanding function pointer - passing it as an argument

    - by Stef
    I want to pass a member function of class A to class B via a function pointer as argument. Please advise whether this road is leading somewhere and help me fill the pothole. #include <iostream> using namespace std; class A{ public: int dosomeA(int x){ cout<< "doing some A to "<<x <<endl; return(0); } }; class B{ public: B(int (*ptr)(int)){ptr(0);}; }; int main() { A a; int (*APtr)(int)=&A::dosomeA; B b(APtr); return 0; } This brilliant piece of code leaves me with the compiler error: cannot convert int (A::*)(int)' toint (*)(int)' in initialization Firstly I want it to compile. Secondly I don't want dosomeA to be STATIC.

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  • Getting input in system() function (Mac)

    - by Alex
    #include <iostream> using namespace std; int main() { short int enterVal; cout << "enter a number to say: " << endl; cin >> enterVal; system("say "%d"") << enterVal; return 0; } Is what I am currently trying. I want the user to enter a number and the system() function says it basically. The code above has an error which says " 'd' was not declared in this scope ". Thanks in advance.

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  • How to get path to current exe file on Linux?

    - by user1519221
    The code below gives current path to exe file on Linux: #include <iostream> std::string getExePath() { char result[ PATH_MAX ]; ssize_t count = readlink( "/proc/self/exe", result, PATH_MAX ); return std::string( result, (count > 0) ? count : 0 ); } int main() { std::cout << getExePath() << std::endl; return 0; } The problem is that when I run it gives me current path to exe and name of the exe, e.g.: /home/.../Test/main.exe I would like to get only /home/.../Test/ I know that I can parse it, but is there any nicer way to do that?

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  • Programmatically find maximum static array size in C++

    - by GuyGreer
    I am curious whether it is possible to determine the maximum size that an array can have in C++. #include <iostream> using namespace std; #define MAX 2000000 int main() { long array[MAX]; cout << "Message" << endl; return 0; } This compiles just fine, but then segfaults as soon as I run it (even though array isn't actually referenced). I know it's the array size too because if I change it to 1000000 it runs just fine. So, is there some define somewhere or some way of having #define MAX MAX_ALLOWED_ARRAY_SIZE_FOR_MY_MACHINE_DEFINED_SOMEWHERE_FOR_ME? I don't actually need this for anything, this question is for curiosity's sake.

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  • Using FILE_FLAG_NO_BUFFERING will return noticeable speed gain?

    - by 9dan
    Recently noticed detail description of FILE_FLAG_NO_BUFFERING flag in MSDN, and read several Google search results about unbuffered I/O in Windows. http://msdn.microsoft.com/en-us/library/aa363858(v=vs.85).aspx I wondering now, is it really important to consider unbuffered option in file I/O programming? Because many programs use plain old C stream I/O or C++ iostream, I didn't gave any attention to FILE_FLAG_NO_BUFFERING flag before. Let's say we are developing photo explorer program like Picasa. If we implement unbuffered I/O, could thumbnail display speed show noticeable difference in ordinary users?

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  • char pointer array in c#

    - by james
    consider the following c++ code #include "stdafx.h" #include<iostream> using namespace std; void ping(int,char* d[]); void ping(int a,char *b[]) { int size; size=sizeof(b)/sizeof(int); // total size of array/size of array data type //cout<<size; for(int i=0;i<=size;i++) cout<<"ping "<<a<<b[i]<<endl; } int _tmain(int argc, _TCHAR* argv[]) { void (*funcptr)(int,char* d[]); char* c[]={"a","b"}; funcptr= ping; funcptr(10,c); return 0; } how can i implement the same in c#.. m new to c#. how can i have char pointer array in c#?

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  • How to split the definition of template friend funtion within template class?

    - by ~joke
    The following example compiles fine but I can't figure out how to separate declaration and definition of operator<<() is this particular case. Every time I try to split the definition friend is causing trouble and gcc complains the operator<<() definition must take exactly one argument. #include <iostream> template <typename T> class Test { public: Test(const T& value) : value_(value) {} template <typename STREAM> friend STREAM& operator<<(STREAM& os, const Test<T>& rhs) { os << rhs.value_; return os; } private: T value_; }; int main() { std::cout << Test<int>(5) << std::endl; }

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  • How to update a vector in method

    - by gurpinars
    I'm new to C++ and trying to understand vectors. My goal is to update a vector in method: #include <vector> #include <iostream> using namespace std; void test(vector<int>& array){ for(int i=0;i<10;i++){ array.push_back(i); } } int main(){ // some integer value vector<int> array(10); test(array); for(int i=0;i<array.size();++i) cout<<array.at(i)<<endl; cout<<"array size:"<<array.size()<<endl; return 0; } output: 0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 5 6 7 8 9 array size:20 I haven't figure out why 10 zeros add vector at first?

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  • Problem with "not declared in this scope" error

    - by lego69
    I've got: error a1 was not declared in this scope Can somebody please explain why this code causes that? quiz.h #ifndef QUIZ_H_ #define QUIZ_H_ #include "quiz.cpp" class A { private: int player; public: A(int initPlayer); ~A(); void foo(); }; #endif /* QUIZ_H_ */ quiz.cpp #include "quiz.h" #include <iostream> using std::cout; using std::endl; A::A(int initPlayer = 0){ player = initPlayer; } A::~A(){ } void A::foo(){ cout << player; } main function #include "quiz.h" int main() { quiz(7); return 0; } quiz function #include "quiz.h" void quiz(int i) { A a1(i); a1.foo(); }

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