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  • Overriding vs Virtual

    - by anonymous
    What is the purpose of using the reserved word virtual in front of functions? If I want a child class to override a parent function, I just declare the same function such as "void draw(){}". class Parent{ public: void say(){ std::cout << "1"; }}; class Child : public Parent{public:void say(){ std::cout << "2"; } }; int main() { Child* a = new Child(); a->say(); return 0; } The output is 2. So again, why would the reserved word "virtual" be necessary in the header of say() ? Thanks a bunch.

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  • How does the below program work in c++?

    - by Srinivasa Varadan
    I have just created 2 pointers which has undefined behavior and try to invoke a class member function which has no object created ? I don't understand this? #include<iostream> using namespace std; class Animal { public: void talk() { cout<<"I am an animal"<<endl; } }; class Dog : public Animal { public: void talk() { cout<<"bark"<<endl; } }; int main() { Animal * a; Dog * d; d->talk(); a->talk(); }

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  • C++ Program performs better when piped

    - by ET1 Nerd
    I haven't done any programming in a decade. I wanted to get back into it, so I made this little pointless program as practice. The easiest way to describe what it does is with output of my --help codeblock: ./prng_bench --help ./prng_bench: usage: ./prng_bench $N $B [$T] This program will generate an N digit base(B) random number until all N digits are the same. Once a repeating N digit base(B) number is found, the following statistics are displayed: -Decimal value of all N digits. -Time & number of tries taken to randomly find. Optionally, this process is repeated T times. When running multiple repititions, averages for all N digit base(B) numbers are displayed at the end, as well as total time and total tries. My "problem" is that when the problem is "easy", say a 3 digit base 10 number, and I have it do a large number of passes the "total time" is less when piped to grep. ie: command ; command |grep took : ./prng_bench 3 10 999999 ; ./prng_bench 3 10 999999|grep took .... Pass# 999999: All 3 base(10) digits = 3 base(10). Time: 0.00005 secs. Tries: 23 It took 191.86701 secs & 99947208 tries to find 999999 repeating 3 digit base(10) numbers. An average of 0.00019 secs & 99 tries was needed to find each one. It took 159.32355 secs & 99947208 tries to find 999999 repeating 3 digit base(10) numbers. If I run the same command many times w/o grep time is always VERY close. I'm using srand(1234) for now, to test. The code between my calls to clock_gettime() for start and stop do not involve any stream manipulation, which would obviously affect time. I realize this is an exercise in futility, but I'd like to know why it behaves this way. Below is heart of the program. Here's a link to the full source on DB if anybody wants to compile and test. https://www.dropbox.com/s/6olqnnjf3unkm2m/prng_bench.cpp clock_gettime() requires -lrt. for (int pass_num=1; pass_num<=passes; pass_num++) { //Executes $passes # of times. clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &temp_time); //get time start_time = timetodouble(temp_time); //convert time to double, store as start_time for(i=1, tries=0; i!=0; tries++) { //loops until 'comparison for' fully completes. counts reps as 'tries'. <------------ for (i=0; i<Ndigits; i++) //Move forward through array. | results[i]=(rand()%base); //assign random num of base to element (digit). | /*for (i=0; i<Ndigits; i++) //---Debug Lines--------------- | std::cout<<" "<<results[i]; //---a LOT of output.---------- | std::cout << "\n"; //---Comment/decoment to disable/enable.*/ // | for (i=Ndigits-1; i>0 && results[i]==results[0]; i--); //Move through array, != element breaks & i!=0, new digits drawn. -| } //If all are equal i will be 0, nested for condition satisfied. -| clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &temp_time); //get time draw_time = (timetodouble(temp_time) - start_time); //convert time to dbl, subtract start_time, set draw_time to diff. total_time += draw_time; //add time for this pass to total. total_tries += tries; //add tries for this pass to total. /*Formated output for each pass: Pass# ---: All -- base(--) digits = -- base(10) Time: ----.---- secs. Tries: ----- (LINE) */ std::cout<<"Pass# "<<std::setw(width_pass)<<pass_num<<": All "<<Ndigits<<" base("<<base<<") digits = " <<std::setw(width_base)<<results[0]<<" base(10). Time: "<<std::setw(width_time)<<draw_time <<" secs. Tries: "<<tries<<"\n"; } if(passes==1) return 0; //No need for totals and averages of 1 pass. /* It took ----.---- secs & ------ tries to find --- repeating -- digit base(--) numbers. (LINE) An average of ---.---- secs & ---- tries was needed to find each one. (LINE)(LINE) */ std::cout<<"It took "<<total_time<<" secs & "<<total_tries<<" tries to find " <<passes<<" repeating "<<Ndigits<<" digit base("<<base<<") numbers.\n" <<"An average of "<<total_time/passes<<" secs & "<<total_tries/passes <<" tries was needed to find each one. \n\n"; return 0;

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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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  • C++ Access variable value using string representing variable's name

    - by Paul Ridgway
    Hello everyone, If the title was not clear, I will try to clarify what I am asking: Imagine I have a variable called counter, I know I can see its current value by doing something like: std::cout << counter << std::endl; However, assume I have lots of variables and I don't know which I'm going to want to look at until runtime. Does anyone know a way I can fetch the value of a variable by using its name, for example: std::cout << valueOf("counter") << std::endl; I feel being able to do this might make debugging large complex projects easier. Thanks in advance for your time. PS: Please do not respond with 'Google it', I have, though maybe not with the best query to get the answer I'm looking for...

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  • Receiving integers, but also want to test for char.

    - by Wayne Haworth
    Say I am looking to receive a series of numeric values and read them into an int, but I also want to test if the user hit key 'x'. I am sure I am missing something obvious, and have tried a few things but seem to be stuck. This is what I have so far... cout << endl << "Enter key (or 'x' to exit): "; cin key; if (key == 'x') { cout << "exiting";} // continue on...

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  • C++ Arrays of Structure access

    - by learningtolive
    Hi, I'm studying C++ from Schildt's book and don't quite understand what does he mean under third structure; Can somebody explain this - To access a specific structure within an array of structures, you must index the structure name. For example, to display the on_hand member of the third structure, you would write cout cout << invtry[2].on_hand; Some code: struct type{ char item[40]; double cost; double retail; int on_hand; int lead_time; }invtry[SIZE];

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  • C++ pointer to functions, Beginner Question...

    - by BobAlmond
    Hi all, I want to ask about pointer in C++ I have some simple code: int add(int a, int b){ return a+b; } int runner(int x,int y, int (*functocall)(int, int)){ return (*functocall)(x,y); } now, suppose I call those functions using this way : cout<<runner(2,5,&add); or maybe cout<<runner(2,5,add); is there any difference? because when I tried, the result is the same and with no error. Thanks a lot

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  • Array not returned correctly

    - by hp1
    I am trying to return a simple array, but I am not getting the correct result. I am getting the following arr1[0] = 1 arr1[1] = 32767 result while the result should have been arr1[0] = 1 arr1[1] = 15 Please suggest. int *sum(int a, int b){ int arr[2]; int *a1; int result = a+b; arr[0]= 1; arr[1]= result; a1 = arr; return a1; } int main(){ int *arr1 = sum(5,10); cout<<"arr1[0] = "<<arr1[0]<<endl; cout<<"arr1[1] = "<<arr1[1]<<endl; return 0; }

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  • C++ beginner question regarding chars

    - by Samwhoo
    I'm just messing around with some C++ at the moment trying to make a simple tic-tac-toe game and I'm running into a bit of a problem. This is my code: #include <iostream> using namespace std; class Square { public: char getState() const; void setState(char); Square(); ~Square(); private: char * pState; }; class Board { public: Board(); ~Board(); void printBoard() const; Square getSquare(short x, short y) const; private: Square board[3][3]; }; int main() { Board board; board.getSquare(1,2).setState('1'); board.printBoard(); return 0; } Square::Square() { pState = new char; *pState = ' '; } Square::~Square() { delete pState; } char Square::getState() const { return *pState; } void Square::setState(char set) { *pState = set; } Board::~Board() { } Board::Board() { } void Board::printBoard() const { for (int x = 0; x < 3; x++) { cout << "|"; for (int y = 0; y < 3; y++) { cout << board[x][y].getState(); } cout << "|" << endl; } } Square Board::getSquare(short x, short y) const { return board[x][y]; } Forgive me if there are blatantly obvious problems with it or it's stupidly written, this is my first program in C++ :p However, the problem is that when I try and set the square 1,2 to the char '1', it doesn't print out as a 1, it prints out as some strange character I didn't recognise. Can anyone tell me why? :) Thanks in advance.

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  • Another problem with decltype

    - by There is nothing we can do
    template<class IntT, IntT low = IntT(), IntT high = IntT()> struct X { static_assert(std::is_same<decltype(low),decltype(high)>::value,"Different types not allowed");//this should give error if types are different decltype(low) a; decltype(high) b; X():a(decltype(a)()),b(decltype(b)())//WHY THIS DOES NOT COMPILE? { cout << typeid(a).name() << '\n'; cout << typeid(b).name() << '\n'; } }; int _tmain(int argc, _TCHAR* argv[]) { X<char,1,'a'> x;//this according to static_assert shouldn't compile but it does return 0; } Using VS2010. Please see 3 comments in code above.

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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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  • C++ STL: Trouble with string iterators

    - by Rosarch
    I'm making a simple command line Hangman game. void Hangman::printStatus() { cout << "Lives remaining: " << livesRemaining << endl; cout << getFormattedAnswer() << endl; } string Hangman::getFormattedAnswer() { return getFormattedAnswerFrom(correctAnswer.begin(), correctAnswer.end()); } string Hangman::getFormattedAnswerFrom(string::const_iterator begin, string::const_iterator end) { return begin == end? "" : displayChar(*begin) + getFormattedAnswerFrom(++begin, end); } char Hangman::displayChar(const char c) { return c; } (Eventually, I'll change this so displayChar() displays a - or a character if the user has guessed it, but for simplicity now I'm just returning everything.) When I build and run this from VS 2010, I get a popup box: Debug Assertion Failed! xstring Line: 78 Expression: string iterator not dereferenceable What am I doing wrong?

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  • How to define a custom iterator in C++

    - by Robert Martin
    I've seen a number of posts on SO about how to define custom iterators, but nothing that seems to exactly answers my question, which is... How do I create an iterator that hides a nested for loop? For instance, I have a class Foo, inside of the Foo is a Bar, and inside of the Bar is a string. I could write for (const Foo& foo : foo_set) for (const Bar& bar : foo.bar_set) if (bar.my_string != "baz") cout << bar.my_string << endl; but instead I want to be able to do something like: for (const string& good : foo_set) cout << good << endl; How do I do something like this?

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  • glReadPixels() returning non-accurate value

    - by max
    I'm trying to implement the flood fill algorithm. But glReadPixels() is returning float RGB values of a pixel which are slightly different from the actual value set by me, causing the algorithm to fail. Why is this happening? Outputting returned RGB values to check. #include<iostream> #include<GL/glut.h> using namespace std; float boundaryColor[3]={0,0,0}, interiorColor[3]={0,0,0.5}, fillColor[3]={1,0,0}; float readPixel[3]; void init(void) { glClearColor(0,0,0.5,0); glMatrixMode(GL_PROJECTION); gluOrtho2D(0,500,0,500); } void setPixel(int x,int y) { glColor3fv(fillColor); glBegin(GL_POINTS); glVertex2f(x,y); glEnd(); } void getPixel(int x, int y, float *color) { glReadPixels(x,y,1,1,GL_RGB,GL_FLOAT,color); } void floodFill(int x,int y) { getPixel(x,y,readPixel); //outputting values here to check cout<<readPixel[0]<<endl; cout<<readPixel[1]<<endl; cout<<readPixel[2]<<endl; if( readPixel[0]==interiorColor[0] && readPixel[1]==interiorColor[1] && readPixel[2]==interiorColor[2] ) { setPixel(x,y); floodFill(x+1,y); floodFill(x,y+1); floodFill(x-1,y); floodFill(x,y-1); } } void display() { glClear(GL_COLOR_BUFFER_BIT); glColor3fv(boundaryColor); glLineWidth(3); glBegin(GL_LINE_STRIP); glVertex2i(150,150); glVertex2i(150,350); glVertex2i(350,350); glVertex2i(350,150); glVertex2i(150,150); glEnd(); floodFill(200,200); glFlush(); } int main(int argc,char** argv) { glutInit(&argc,argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutInitWindowPosition(100,100); glutInitWindowSize(500,500); glutCreateWindow("Flood fill"); init(); glutDisplayFunc(display); glutMainLoop(); }

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  • C++ open() fails for no apparant reason

    - by jondoe
    The following code: char filename[64]; ifstream input; cout << "Please enter the filename: " << endl; cin >> filename; input.open(filename); if (!input.is_open()) { cout << "Opening file " << filename << " failed." << endl; exit(1); } fails, it enters the if() and exits. What could possibly be the cause for this? I'm using Microsoft Visual C++. When I hardcoded the filename as a constant it instead ended up garbled: http://pici.se/pictures/CNQEnwhgo.png Suggestions?

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  • Why is the destructor of the class called twice ?

    - by dicaprio
    Apologies if the question sounds silly, I was following experts in SO and trying some examples myself, and this is one of them. I did try the search option but didn't find an answer for this kind. class A { public: A(){cout<<"A Contruction"<<endl;} ~A(){cout<<"A destruction"<<endl;} }; int main() { vector<A> t; t.push_back(A()); // After this line, when the scope of the object is lost. } Why is the destructor of the class called twice ?

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  • Why is this C++ code working ?

    - by gregseth
    Why doesn't the program segfault on the p->info() call? struct A { int info() { retrun (this) ? 1 : -1; } }; int main() { A* p = NULL; if (p->info() == 1) { cout << "I'm alive!" << endl; } else { cout << "I'm NULL..." << endl; } return 0; }

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  • How to know if the argument that is passed to the function is a class, union or enum in c++?

    - by Narek
    I want to define an operator<< for all enums, to cout the value and print that it is an enum like this: code: enum AnyEnum{A,B,C}; AnyEnum enm = A; cout << enm <<endl; output: This is an enum which has a value equal to 0 I know a way of doing this with Boost library by using is_enum struct. But I don’t understand how it works. So that's why, in general, I am interested how to identify if the veriable is a class type, union type or an enum (in compile time).

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  • Need help with map (c++, STL)

    - by Mike Dooley
    Hi folks! Actually I'm new to C++. I tried something out (actually the map container) but it doesn't work the way I assumed it will... Before posting my code, I will explain it shortly. I created 3 classes: ClassA ClassDerivedA ClassAnotherDerivedA The two last ones are derived from "ClassA". Further I created a map: map<string,ClassA> test_map; I put some objects (from Type ClassDerivedA and ClassAnotherDerivedA) into the map. Keep in mind: the mapped value is from type "ClassA". This will only work because of Polymorphism. Finally I created an iterator which runs over my map and compares the user input with my keys in the map. If they match, it will call a specific method called "printOutput". And there is the Problem: Although i declared "printOutput" as "virtual" the only method called is the one from my base class, but why? and here is the code: #include <iostream> #include <map> using namespace std; class ClassA { public: virtual void printOutput() { cout << "ClassA" << endl; } }; class ClassDerivedA : public ClassA { public: void printOutput() { cout << "ClassDerivedA" << endl; } }; class ClassAnotherDerivedA: public ClassA { public: void printOutput() { cout << "ClassAnotherDerivedA" << endl; } }; int main() { ClassDerivedA class_derived_a; ClassAnotherDerivedA class_another_a; map<string,ClassA> test_map; test_map.insert(pair<string,ClassA>("deriveda", class_derived_a)); test_map.insert(pair<string,ClassA>("anothera", class_another_a)); string s; while( cin >> s ) { if( s != "quit" ) { map<string,ClassA>::iterator it = test_map.find(s); if(it != test_map.end()) it->second.printOutput(); } else break; } } Blockquote

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  • how to take input for uint32_t variable

    - by sksingh73
    i have declared a variable as uint32_t num; when i take input for this variable i.e cinnum; cout< when i run this program, i gives num value as 12345678, it works fine & give cout. but when i give input as 1234abcd. it creates problem & displays only 1234. please suggest solution to resolve this problem.

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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 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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  • array of objects of a class

    - by anurag18294
    #include class test{ int a; char b; public: test() { cout<<"\n\nDefault constructor being called"; } test(int i,char j) { a=i; b=j; cout<<"\n\nConstructor with arguments called"; } }; int main() { test tarray[5]; test newobj(31,'z'); }; In the above code snippet can we intialize values to tarray[5].

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  • C++: Print only one char

    - by Martijn Courteaux
    Hi, When I read one char* from std::cin and I want to write it to std::cout, it prints until it finds a \0 in memory. So what did was: char c; cin >> c; char* pChar = &c; pChar++; *pChar = '\0'; println(&c); // My own method: void println(char * str) { cout << str << endl; } But I don't think this is a safe action. Is there a safer way to do this?

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