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General C++ Programming - December 2021

Get updated and ready for important C++ exercises

Hello all, I'm an experienced C++ programmer with the absence about a year from it. Now I should recall and update my understandings of C++ to its current stan...

[1 reply] : I would recommend the exercises from B. Stroustrup's book. https://ww... (by thmm)

by Cambalinho

Math: how calculate the line dots?

the line have origin and destion points. how can i calculate the dots between the line origin and destination. i create these code: #include <iostream> #in...

[15 replies] Last: 3D Rotation: https://imgur.com/qOgUuPf 2D Rotation: https://imgur.com... (by Cambalinho)

by closed account G21UpDi1

fastest find and replace for a string (1,2,3)

This is how I'm doing it; is there a faster way? The program could do it millions of times, so I expect any time savings would improve it. std::regex dou...

[59 replies] Last: Here is a search and replace (SAR) by simple string indexing. I use a... (by oggin)

by lastchance

Eigen is not fast??

(Edit - OP has vanished: or been assisted to depart) Well, dividing by 0 is quite fast ... if not very enlightening. Matrix3d m2; m2 << 1, 2, 3, 4, 5, 6, 7...

[3 replies] Last: I guess the OP has vanished, but Eigen is likely to benefit substantia... (by mbozzi)

by Cplusc

Sparse Matrix transpose

hello everyone. I have a matrix in which most of the elements are zero. For efficiency purpose, I stored this matrix in csr format(Compressed row storage). Now ...

[16 replies] Last: ...and now the transpose is ridiculously easy. :O) (by Duthomhas)

by baezacaljo

How to avoid dynamic memory allocation, and templates for matricez using Eigen library in C++

Hello dear all Look i am using the library Eigen, for Matrix and vector calculations. when, i tried to generate a matrix using advance initialization i want t...

[8 replies] Last: Jonnin, i never got such an nice answer telling the truth, Thank you v... (by baezacaljo)

by algmaster

how to find the highest sum of a subsequence

How to write a program in C++ to find the highest sum of subsequence elements of a given sequence? At the input, the user gives the length of the sequence and t...

[5 replies] Last: #include <iostream> #include <vector> using namespace std; int bestS... (by lastchance)

by frek

Range based for loop

Doesn't mean for (const auto& x : v) { /* do something with the value of x */ } this for (auto x : v) { /* do something with the value of x */ } supposing v...

[4 replies] Last: ^^^ that is a whole new discussion, but the & means that changes (if y... (by jonnin)

by uppercaseguy

object not dynamically allocating

when i try to allocate new memory of an object of structure type, it gives a "read access violation" error. ftn that does that Voter* create_voter_node(s...

[8 replies] Last: I assume @seeplus is asking about line 7 of the first snippet of code ... (by mbozzi)

by Cplusc

Vector indexing

Hi everyone. Is there any way to give arbitrary indexing to a vector? For example I have a vector a={1,5,6,2,7,0}. Now the indeces are 0,1,2,3,4,5. I want the i...

[10 replies] Last: A trivial method: #include <vector> #include<string> #include<iost... (by oggin)

by dobbijs

Check input time format

Hello! I had a task - The program requests time in the format hh: mm: ss and checks the correctness of the input. I have created the code, but entering the exam...

[3 replies] Last: This works with VS: #include <iostream> #include <string> #include ... (by seeplus)

by Cplusc

MPI_Allreduce for object of a class

Let's say I have a class named Node. A user defined vector of objects of this class is std::vector<Node> Nodes. Each Part of this vector is built in different p...

[3 replies] Last: Thanks for your answers. It was helpful. (by Cplusc)

by arnesc

tableprinter - Table-like output

I have written a small library with the help of iomanip and ostream header which allows a programmer to print table-like data. I am using this table-like format...

[5 replies] Last: Thank you :) I refactored function object passing part and made value... (by arnesc)

by thecoolbeast

Recursion Function

Hello, currently im working on a homework problem that deals with recursion, the problem goes as follows: Suppose you can buy chocolate bars from a vending mac...

[10 replies] Last: Thanks! I believe Line 21 should have read return money + get_bars_1... (by mbozzi)

by The apprentice

Help C++

First, I wish you all a good day. I'm trying to solve some problems in c ++ (I think it's important to let me know that I'm still a beginner and I don't unde...

[2 replies] Last: @The apprentice, PLEASE USE CODE TAGS (the <> formatting button to ... (by JRManx)

by baezacaljo

Generate a template class for a Matrix using vectors or change to Eigen library, C++

Hello dear all i am new using this forum. i have a question look, i have a project on which we are using several classes, therefore also several "Matrices", ...

[17 replies] Last: Thanks jonnin, I got it. Also, I searched for some info, and now I hav... (by baezacaljo)

by Cplusc

MPI

Let say I have a vector of vector in my master processor. I want to assign each vector to its corresponding processor. for example the first processor will just...

[9 replies] Last: sorry, I didn't provide a good example of my question. (by Cplusc)

by Hachiman

Pointer Arrays

This is the pseudocode for the project: Declare the following prototypes : int sumSales(int list , int size); int winnerIndex(int list , int size); ...

[7 replies] Last: they may work. its hard to say. you throw away the returned values! ... (by jonnin)

by ryuuki

alternating values

hi can you help me. i want to have my value in 2nd column under x1, ek0 and ek2 will become the value of my ek0, ek1, and ek2 instead this is the part of the...

[6 replies] Last: Thank you very much! I am just a beginner to this and just modifying e... (by ryuuki)

by closed account EUoNwbRD

How to get the type of a variable without the "typeinfo" header?

I don't want to link the C++ (not even C's libc) and I want to learn how (and if) I can get the type of a variable for a comparison. For example I want to do so...

[17 replies] Last: Honestly, I don't see why it shouldn't be allowed to post on differen... (by jonnin)

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