Most viewed questions in C++

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declaring a priority_queue in c++ with a custom comparator

I'm attempting to declare a priority queue of nodes using the comparator function bool Compare(Node a, Node b) (which is outside the node class). I presently have the following: priority_queue<Node, vector<Node>, Compare> openSet; I'm receiving Error: "Compare" is not a type name for some reason. Adding priority_queue<Node, vector Node>, bool Compare> to the declaration. gives me the error 'Error: expecting a '>' I've also attempted: priority_queue<Node, vector<Node>, Compare()> openSet; priority_queue<Node, ...READ MORE

Aug 11, 2022 in C++ by Nicholas
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1,494 views
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Is there an easy way to make a min heap in C++?

Use make heap() and its buddies from algorithm>, or priority queue from queue>.  Make heap and friends are used by priority queue. #include <queue> // functional,iostream,ctime,cstdlib using namespace std; int main(int ...READ MORE

Jun 27, 2022 in C++ by Damon
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1,492 views
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outputting ascii table in C++

This line doesn't do the right thing: ch ...READ MORE

Jun 13, 2022 in C++ by Damon
• 4,960 points
1,468 views
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1 answer

Ternary operator ?: vs if...else

It's not any faster.  There is one difference when you can initialize a constant variable using an expression: const int x = (a<b) ? b ...READ MORE

Jun 7, 2022 in C++ by Damon
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1,452 views
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Easiest way to convert int to string in C++

std::stoi (and variations for each numeric type) ...READ MORE

Jun 15, 2022 in C++ by Damon
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1,451 views
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C++ convert from 1 char to string?

I simply need to cast one character to string.  The inverse method is as easy as str[0]. The following suggestions did not work for me: char c = 34; string(1,c); //this doesn't work, the ...READ MORE

Jun 29, 2022 in C++ by Damon
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1,444 views
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The Definitive C++ Book Guide and List

For Beginner (includes those without coding experience) Programming: ...READ MORE

Jun 6, 2022 in C++ by pranav
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1,443 views
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How do I create an array of pointers?

Student** db = new Student*[5]; // To allocate ...READ MORE

Aug 5, 2022 in C++ by Damon
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1,432 views
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Best way to split a vector into two smaller arrays?

I'm attempting to divide a vector into ...READ MORE

Nov 17, 2022 in C++ by Ashwini
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1,425 views
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What does Tokens do and why they need to be created in C++ programming?

Tokenization is essential in determining what a programme does.  What Bjarne is referring to in respect to C++ code is how tokenization rules alter the meaning of a programme.  We need to know what the tokens are and how they are determined.  Specifically, how can we recognise a single token when it comes among other characters, and how should tokens be delimited if  there is ambiguity? Consider the prefix operators ++ and +, for example. Assume we have just one token + to deal with.  What does the following excerpt mean? int i = 1; ++i; Is the above going to apply unary + on i twice with + only? Or will it only increase it once? Naturally, it's vague.  We require an additional token, thus ++ is introduced as its own "word" in the language. But there is now another (though minor) issue.  What if the programmer just wants to use unary + twice without incrementing?  Rules for token processing are required.  So, if we discover that a white space is always used as a token separator, our programmer may write: int i ...READ MORE

Aug 2, 2022 in C++ by Damon
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1,415 views
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lower_bound == upper_bound

Lower bound: the initial greater-or-equal element. Upper bound: ...READ MORE

Jun 21, 2022 in C++ by Damon
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1,387 views
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Why is "using namespace std;" considered bad practice?

This has nothing to do with performan ...READ MORE

Jun 1, 2022 in C++ by Damon
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1,379 views
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1 answer

str_lib_facilities.h file from Stroustrup's Programming: Principles and Practice Using C++ generating errors

Switching the compiler to compile in c++11 ...READ MORE

Jun 13, 2022 in C++ by Damon
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1,374 views
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std::string length() and size() member functions

While reading the responses to this topic, ...READ MORE

Aug 5, 2022 in C++ by Nicholas
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1,370 views
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1 answer

Using getline() in C++

If you use getline() after cin >> anything, you must first flush the newline character from the buffer.  You can achieve this by using the cin.ignore() It would be something like this: string messageVar; cout ...READ MORE

Jun 1, 2022 in C++ by Damon
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1,370 views
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How to Access Subgraphs of an Existing Graph in Boost

I read a graph using read graphviz() ...READ MORE

Aug 11, 2022 in C++ by Nicholas
• 7,760 points
1,365 views
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1 answer

What is the best way to use a HashMap in C++?

The ordered and unordered map containers (std::map and std::unordered map) are included in the standard library.  The items in an ordered map are sorted by key, and insert and access are in O (log n).  For ordered maps, the standard library often use red black trees.  However, this is only an implementation detail.  Insert and access are in O in an unordered map (1).  It is simply another term for a hashtable. An illustration using (ordered) std::map: #include <map> #include <iostream> #include <cassert> int main(int argc, char ...READ MORE

Jun 10, 2022 in C++ by Damon
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1,349 views
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Sorting vector elements in descending order

Because of the goto reset instruction, I believe your sort function has entered an infinite loop.  If you wish to construct a basic bubble-sort algorithm, follow these steps: #include <iostream> #include <utility> #include <vector> void bubble_sort(std::vector<int>& v) { ...READ MORE

Jul 11, 2022 in C++ by Damon
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1,347 views
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1 answer

Suggestions of excellent examples of real C/C++ code

I'd like to particularly bring up memcached.  ...READ MORE

Dec 17, 2022 in C++ by narikkadan
• 86,360 points
1,325 views
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1 answer

Error "Microsoft Visual C++ 14.0 is required (Unable to find vcvarsall.bat)"

For pip, use the binary-only option.  ...READ MORE

Jun 14, 2022 in C++ by Damon
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1,317 views
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std::cin input with spaces?

#include <string> std::string input; std::cin >> input; The user want to type "Hello World."  However, cin fails to recognise the space between the two words.  How do I get Cin to see the entire Hello World? I'm trying this using structs, and cin.getline doesn't appear to work.  This is my code: struct cd { ...READ MORE

Aug 11, 2022 in C++ by Nicholas
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1,283 views
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1 answer

implementing merge sort in C++

To respond to the question:  std::vectorT> is used to create dynamically sized arrays at runtime.  Ideally, you'd use one of these to get feedback.  If not, they are simple to convert.  For instance, you might make two arrays like this: template <typename T> void merge_sort(std::vector<T>& array) { ...READ MORE

Jun 10, 2022 in C++ by Damon
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1,281 views
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1 answer

How to pass in command line arguments when using ideone?

It appears that you won't be able ...READ MORE

Jun 21, 2022 in C++ by Damon
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1,280 views
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C++ Switch Cases

I was taking an online quiz based on the C++ switch statement.  I came across a question, and while I have a good knowledge of how switch statements function, this particular question made no sense to me.  Could you please explain? Why is the answer D and not ...READ MORE

Jul 22, 2022 in C++ by Nicholas
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1,277 views
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How to make an array with a dynamic size? General usage of dynamic arrays (maybe pointers too)?

I wanna create a program that can ...READ MORE

Aug 5, 2022 in C++ by krishna
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1,274 views
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1 answer

why are copy constructors needed and what are the cases where they are very helpful?

A copy constructor is a member function ...READ MORE

May 31, 2022 in C++ by Damon
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1,273 views
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Intersection of two std::unordered_map

I have two std::unordered_map std::unordered_map<int, int> mp1; std::unordered_map<int, int> ...READ MORE

May 31, 2022 in C++ by Nicholas
• 7,760 points
1,258 views
0 votes
1 answer

What data structure is inside std::map in C++?

An associative container is std::map. The standard's ...READ MORE

May 31, 2022 in C++ by Damon
• 4,960 points
1,250 views
0 votes
1 answer

What range of values can integer types store in C++

You may rely on the following minimal ...READ MORE

Jun 21, 2022 in C++ by Damon
• 4,960 points
1,230 views
0 votes
1 answer

Simple linked list in C++

This is the most basic example I can think of in this situation, and it has not been tested.  Please keep in mind that this violates some C++ best practises and deviates from the norm (initialize lists, separation of declaration and definition, and so on).  But those aren't topics I can discuss here. #include <iostream> using namespace std; class LinkedList{ ...READ MORE

Jun 2, 2022 in C++ by Damon
• 4,960 points
1,224 views
0 votes
1 answer

insert method for doubly linked list C++

I attempted to repair all of your methods, and I believe I succeeded; at least, the current test example prints the proper answer: #include <iostream> #include <vector> using namespace std; struct Node { ...READ MORE

Jun 21, 2022 in C++ by Damon
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1,220 views
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1 answer

Why does C++ need the scope resolution operator?

No. There is no scope resolution operator ...READ MORE

Jun 1, 2022 in C++ by Damon
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1,215 views
0 votes
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How can I get double quotes into a string literal?

I used the printf() command to produce the output seen below: printf("She said time flies like an arrow, ...READ MORE

Aug 5, 2022 in C++ by Nicholas
• 7,760 points
1,194 views
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Making a class abstract without any pure virtual methods

I take a class where we watch ...READ MORE

Aug 17, 2022 in C++ by Nicholas
• 7,760 points
1,177 views
0 votes
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What is the difference between ifstream, ofstream and fstream?

I stumbled discovered ifstream, ofstream, and fstream ...READ MORE

Jul 11, 2022 in C++ by Nicholas
• 7,760 points
1,176 views
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C++ - upcasting and downcasting

As an example: Shouldn't the second d.print() call during upcasting print "base"? Isn't it a "d" derived object that has been upcasted to a base class object? And what advantages does downcasting have? Could you describe upcast and downcast in more detail? #include <iostream> using namespace std; class Base { public: ...READ MORE

Jul 26, 2022 in C++ by Nicholas
• 7,760 points
1,164 views
+1 vote
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Parse (split) a string in C++ using string delimiter (standard C++)

In C++, I'm processing a string like follows: using namespace std; string parsed,input="text to be parsed"; stringstream ...READ MORE

Jul 4, 2022 in C++ by Nicholas
• 7,760 points
1,164 views
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Which is better way to calculate nCr

Approach 1: C(n,r) = n!/(n-r)!r! Approach 2:  I discovered this in Wilf's book Combinatorial Algorithms: C(n,r) may be represented as C(n-1,r) + C (n-1,r-1). e.g. C(7,4) = C(6,4) + ...READ MORE

Jul 25, 2022 in C++ by Nicholas
• 7,760 points
1,154 views
0 votes
1 answer

please help me with max_element function in c++ stl

You can substitute max for *max eleme ...READ MORE

Jun 27, 2022 in C++ by Damon
• 4,960 points
1,152 views
0 votes
0 answers

Conversion of base 10 to base 6

I attempted to convert a base 10 number to a base 6 number in C, but my code failed two hidden test cases. I don't see any logical flaws in it. Could you do it? //convert base 10 to base 6 #include<stdio.h> int main() { ...READ MORE

Jul 26, 2022 in C++ by Nicholas
• 7,760 points
1,140 views
0 votes
1 answer

*this vs this in C++

This is a pointer, and *this is a pointer that has been dereferenced. If you had a function that returned this, it would be a pointer to the current object, but a function that returned *this would be a "clone" of the current object, created on the stack unless you defined the method's return type to be a reference. A small application that demonstrates the difference between working with copies and working with references: #include <iostream> class Foo { public: ...READ MORE

Jun 28, 2022 in C++ by Damon
• 4,960 points
1,140 views
0 votes
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When and why do I need to use cin.ignore() in C++?

In C++, I developed a simple application that requested the user to enter a number and then a string.  Surprisingly, when I ran the application, it never paused to ask for the string.  It simply ignored it.  After conducting some research on StackOverflow, I discovered that I needed to include the following line: cin.ignore(256, '\n'); before the line with the string input  That addressed the problem and allowed the software to run.  My issue is why C++ need the cin.ignore() line, and how can I forecast when I will need to use it. Here's the software I created: #include <iostream> #include <string> using namespace std; int main() { ...READ MORE

Jul 4, 2022 in C++ by Nicholas
• 7,760 points
1,137 views
0 votes
1 answer

Create a reverse LinkedList in C++ from a given LinkedList

A simpler solution is to just let the current node point to the previous node while going through your linked list, saving the previous and next nodes as you go. void LinkedList::reversedLinkedList() { if(head == ...READ MORE

Aug 5, 2022 in C++ by Damon
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1,125 views
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Infix to Postfix notation C++

Hello there, Stack.  I'm currently learning C++ and trying to create an RPN converter.  But I'm having difficulties.  Hopefully, I'll be able to describe the issues in detail.  For stacking my operators, I'm using an array.  Let's look at the example "5 + 8."  When it comes down to: else if(infix[i] == '+' or infix[i] == ...READ MORE

Jun 29, 2022 in C++ by Nicholas
• 7,760 points
1,122 views
0 votes
1 answer

C++ - Overloading vs Overriding in Inheritance

In C++, a derived class's method only overrides the base class's method if their declarations match (I say "match," but I'm not sure what the formal term is).  That is, all arguments must be of the same type, with the same const qualification.  If there are any mismatches, the derived class's method hides all methods with the same name rather than overriding.  This is what the "ERROR" in your image is attempting to convey.  So, in that image, / overrides in a comment is incorrect and misleading. Yes, many C++ instructors are unaware of these somewhat esoteric details. Furthermore, if you want to override, your base class's method must be virtual; otherwise, polymorphism will not work. . We could also say that the derived-class method hides the base-class method if it wasn't virtual.  The part about hiding, on the other hand, has almost no meaning here; what this term really means is that you're not in charge. Furthermore, overloading is the presence of multiple methods with the same name but different signatures, as you may have noticed. To be useful, they must all be present in the derived class; otherwise, they will be hidden if the derived class only has one method, fa1, and the other fa1 are in the base. There is, however, a syntax sugar that "copies" all fa1 from base to derived, removing all the hidden semantics: class A { public: void fa1(); ...READ MORE

Jun 7, 2022 in C++ by Damon
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1,113 views
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Read whole ASCII file into C++ std::string

I need to load an entire file ...READ MORE

Aug 23, 2022 in C++ by Nicholas
• 7,760 points
1,106 views
0 votes
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Is there a maxheap in the C++ standard library?

I understand that the std::priority queue class ...READ MORE

Aug 11, 2022 in C++ by Nicholas
• 7,760 points
1,106 views
0 votes
0 answers

How to use setprecision in C++

I'm new to C++ and all I want to do is print my point number up to two digits.  For example, if the number is 3.444, the output should be 3.44, and if the number is 99999.4234, the output should be 99999.42.  How am I going to do that?  The value changes over time.  This is my code. #include <iomanip.h> #include <iomanip> int main() { ...READ MORE

Jul 5, 2022 in C++ by Nicholas
• 7,760 points
1,089 views
0 votes
1 answer

What is the difference between public, private, and protected inheritance in C++?

To begin answering that question, let me characterise member accessors in my own terms.  If you already know this, proceed to the section "next:". I'm aware of three types of accessors: public, protected, and private. Let: class Base { public: ...READ MORE

Jul 11, 2022 in C++ by Damon
• 4,960 points
1,087 views
0 votes
1 answer

How do I reverse a C++ vector?

The algorithm header has a method std::reverse for this purpose. #include <vector> #include <algorithm> int main() { std::vector<int> ...READ MORE

Jun 27, 2022 in C++ by Damon
• 4,960 points
1,086 views