I am attempting to combine two vectors into a vector of pairs. I want to be able to alter the first and second of each pair and have those alterations reflected in the original vectors. I thought the following code might work but get compilation errors about a lack of viable overload for "=" for the line with the call to std::transform:
void f()
{
std::vector<int> a = {1,2,3,4,5};
std::vector<int> b = {6,7,8,9,0};
[Code].....
Say I have a vector of objects and I want to return an object based on a pair of strings. The strings can be in either order Ie; A B==B A.
In general, what do you think is the best way to do this?
I have a project to do in C and coming form Java I miss all the included features that are missing from C! I need to be able to store key value pairs in an quick and memory efficient manner. I've looked up using hash maps but I'm very new to C so don't really understand even the basic ones. I've looked at using a multi-dimensional array as I'm more comfortable with arrays but I'm unsure if that would count as a memory efficient and quick method?
View 14 Replies View RelatedI need numbers next to each other to be sorted (in increasing order).On the CPU I'd do something like this:
for(int i=0; i < length; i+=2) {
if(a[i]>a[i+1]) {
switch places...
}
}
But how would I do this using parallel_for_each (C++AMP) ? I need this for some algorithm that works with very long arrays and I think GPU would do this faster than CPU (even if I use all threads).
Alexandra has some distinct integer numbers a1,a2...an.
Count number of pairs (i,j) such that:
1≤ i ≤ n
1≤ j ≤ n
ai < aj
Input
The first line of the input contains an integer T denoting the number of test cases. The description of T test cases follows. The first line of each test case contains a single integer n denoting the number of numbers Alexandra has. The second line contains n space-separated distinct integers a1, a2, ..., an denoting these numbers.
Output
For each test case, output a single line containing number of pairs for corresponding test case.
Constraints
1 ≤ T ≤ 4
1 ≤ n ≤ 100000
0 ≤ ai ≤ 109
All the ai are distinct
Example
2
2
2 1
3
3 1 2
Output:
1
3
Explanation
Case 1: Only one such pair: (2,1)
Case 2: 3 possible pairs: (2,1), (2,3), (3,1)
as I understand the problem is just counting how many Ai's are 1 <= Ai <= N and then apply ((R*(R-1))/2), R is the count of valid Ai's
My actual code is
#include <stdio.h>
using namespace std;
#ifndef ONLINE_JUDGE
#define getNumber getchar()
#define getString getchar()
[Code] ....
I am working with cart algorithm and i have the following problem,i need to try all possible splits of n values in order to determine the best.
So lets say i have 3 values("low","medium",high) then the possible splits(pairs) would be:
(assuming low=0,medium=1,high=2)
0,1-2 low,medium-high
1,0-2 medium,low-high
2,1-0 high,medium-low
For 4 values(a,b,c,d) it would be:
ab,cd
ac,bd
ad,bc
abc,d
adb,c
adc,b
bcd,a
Problem is i dont know n so the solution must be recursive. The possible splits are 2^(n-1)-1. I am really stuck and most of the code is complete for cart and i really don't want to restrict it to binary values.
coming from Java, my experience with the Classes in C++ is quite limited.
Thats why I am having trouble converting the following (simple!) Java-Program.
Most examples with linked lists I found on the web describe how to implement the LinkedList class itself. But my problem is different: I want to use such a Class (I have a LinkedList class available on my system which is presumably OK).
Code: package main;
import java.util.ArrayList;
public class Main {
public static void main(String[] args) {
BoxList<String> sl = new BoxList<String>(
new ArrayList<ABox<String>>());
sl.getList().add(
new BoxPair2<String>(new BoxPair2<String>(
[code].....
I'm trying to write a simple program that finds the minimum difference between two pairs of integers in a list/array. Of no surprise, it not work the first time I ran it so naturally i chucked in a whole bunch of print statements to debug
I encountered a peculiar error that is really stumping me.
#include <iostream>
using namespace std;
int closest_pair(int arr[]) {
int i=0;
int j=0;
int size=0;
int min=0;
[Code] .....
OUTPUT:
size_main: 20
arr_main: 80
arr[0]_main: 4
size: 2
arr: 8
arr[0]: 4
0: 34
1: -12
2: 18
3: 61
19: 75
closest_pair: 0
I'm printing the size of the array in main and inside the function...and inside the function its giving me a size = 2 which is incorrect though the size printed in main is correct (size = 20). I further narrowed down the discrepancy to this statement: sizeof(arr)
I have been writing a program to generate pairs of RSA keys using small prime numbers. I have been using mpz_invert() to get a value for d for the private key. On small prime numbers it calculates the correct value, but on larger primes it calculates incorrect values.
I'm assuming there must be an upper limit to the values the mpz_invert() function can handle? If so, what is this limit to avoid erroneous values?
Did a little Googling on this but couldn't find anything definitive. Is it safe to do something like
Code:
void MyClass::myFunc(){
my_type_t &foo = some_obj->get_member_reference();
store_for_later(&foo);
}
Then at some pointer later in execution, another function uses the pointer passed to store_for_later.
I have the following code segment:
Code:
void Swap(Number& num1, Number& num2)
{
cout<<"Before swap:"<<num1<<" "<<num2<<endl;
Number& temp=num1;
num1=num2;
num2=temp;
cout<<"After swap:"<<num1<<" "<<num2<<endl;
}
[code]...
to which the output is:
Code:
Before swap:13 11
After swap:13 11
13 11 that seems confusing.
why doesn't Swap() swap the two Numbers?
I am trying to make a utility program for work that will update multiple projects with local dll references. Basically I work with two solutions (for talk sake solutIon1 and solutIon2). Generally solutIon1 will reference the dll's built In solutIon2 which reside on a server. However for debugging proposes I sometimes need to D/L the solutIon2 projects and build them local-ally, so that I can reference the solutIon2 dll's local-ally (this Is so that I can easily attach the dll and step Into the code). However this require changing the reference paths, so that I am pointing to the local-ally built dll's, which Is quite a laborious task.
So the question is how would I update references in solution1 from the program that I am making. I don't really know what to start reading about as I have never done anything like this before.
Is it permissible to declare, for example, `std::valarray<int&>`? If so, how do I initialize such if the `valarray` is a class member?
View 3 Replies View RelatedWhat rvalue references are? How are they useful? What are temporary objects?
View 1 Replies View RelatedI am checking to see if two references are bound to the same object. My instincts tell Me, "Check their addresses. If they match, they are bound to the same." At the same time, I have not found anything in the C++ standard which would support this approach. Am I missing something? Is there wording which backs up My instincts? Is there a standard function to do this?
View 4 Replies View RelatedI have this basic prototype:
struct int_wrapper{int i;};
template <const int_wrapper&... IPack>
void display_all(const int_wrapper&, IPack...);
But when I try to compile it, the compiler says IPack is not a type on the last line. Are packs of references not allowed?
I was wondering if there is way to convert a C# class to its own project and it automatically keeps its references.
View 3 Replies View RelatedIs it possible to create a class that stores (non-const) references to some objects and enables users direct access by using range-based for loops on them?
Code: class container {
public:
void add(int& value);
void remove(int& value);
...
};
int main()
{
container c;
for (auto& value:c) {
// `value' should be accessible as type `int&' instead of being a pointer, `std::reference_wrapper<int>' or something like that
}
}
I'm having some problems in understanding how the code below works and why it produces the output it produces.. What I'd expect is that both functions, namely `add_1' and `add_2', would print the same output; but I've been proven wrong :/ So why does the second one get different memory addresses for the same variable?
Code should be self-explaining:
Code: template<typename... Types>
void add_1(Types&&... values)
{
// by the way: why do i have to use `const int' instead of `int'?
std::vector<std::reference_wrapper<const int>> vector{
std::forward<Types>(values)...};
std::cout << "add_1:" << std::endl;
for (const auto& value:vector) {
std::cout << &value.get() << std::endl;
[code].....
I have an abstract class named Terrain, and a class named RoadMap, which supposed to hold an N*N array of Terrains. But I'm not sure what type should the RoadMap class hold:
Code:
#ifndef TERRAIN_H
#define TERRAIN_H
class Terrain {
[Code] ....
I can't use an array of refernces here, so I tried this:
Code: Terrain** terrain; and then I thought this was the way to go:
Code: Terrain (*terrain)[]; But now I'm not sure.
The N*N matrix size supposed to be determined according to a given input... What type should I use there?
#include "stdafx.h"
#include <iostream>
#include <math.h>
#include <time.h>
#include<iomanip>
#include<array>
#include <algorithm>
using namespace std;
const int AS = 6;
void FillingRandomly(int (*)[AS]);
void printing(int (*)[AS]);
[Code] ....
Basically I have to create an array, fill it, and then print it on screen. The tricky thing is that need to use pointers to fill it and print and later on sort it. My problem is that with this code is that i get
Error2error C2109: subscript requires array or pointer typec:userspcdesktopusbanthonydocumentsvisual studio 2012projectsessaieessaieessaie.cpp55
and
5IntelliSense: expression must have pointer-to-object typec:UserspcDesktopUSBAnthonyDocumentsVisual Studio 2012ProjectsEssaieEssaieEssaie.cpp55
Whenever I try to run it.
I am trying to understand RValue-references as return values of functions. First let's consider a simple function, that transforms a string into upper case letters.
const std::string
toUpper(std::string orig) {
std::transform(orig.begin(), orig.end(), orig.begin(), ::toupper);
return orig;
[Code] .....
It compiles, but I get the output 0 . Here I am wondering why the code above does not move the substr correctly while the code below does (prints out 1):
const std::string&&
no_sense(std::string abc) {
abc = abc.substr(1, 1);
return std::move(abc);
[Code] .....
In both cases abc is a temporary object inside of the function and gets deleted after the function is left. But why does the second version work and the first one does not?
cat.substr(1, 1)
And as my last question. Why doesn't
return std::move(abc.substr(1, 1));
work?
Why cant a dynamic memory allocation work with references? I was told that references work with const pointers deep down so shouldn't this be legal code?
int &&a=new int;
My compiler says that a entity of int* cannot be used to initialize a entity of int&&?
Does that mean that the compiler thinks of them as different types except deep down a reference is implemented with a pointer? Is this right?
I'm looking to implement a Database Access Layer for the project I'm working on, it's a mature project and I'm trying to simplify the database access and as far as possible and remove the Database logic from the Business logic.
Bringing in an ORM solution isn't an option at the moment so I'm looking at bringing in DAO objects to break the coupling. The problem I can't get around in my head is how to avoid Cyclic references
We currently have 2 projects
BL contains types such as Customer, Component and Product which need saving to the Database, the Database project can't know about these items or it would create the cyclic dependency.
I tried adding Dao items to the DB project to mirror these items and to also mirror the DB structure but that requires that the BL project knows how to convert between it's own types and the DAO types which is something I'd like to avoid.
I also tried inserting a third intermediate project that would control the conversion and saving, I called it my DAL project and tried adding functions that would take the BL item and perform CRUD operations but again I ran into the cyclic dependency issue.
My ideal solution would be that the BL project would just have to call a function along the lines of "SaveCustomer(Customer inCustomer)" and not have to worry about doing any conversion.
Is there a project structure that would allow for this?
Is there a point in dynamically creating a pointer during runtime only to dereference it? (if that is the right term, as in *pointer, depoint it?)
In this case should I perhaps store pointers instead of references?
Inventory.cpp
Code:
bool Inventory::addItem(InventoryItem& item) {
addItemAmount(item);
if (item.getAmount() > 0) {
if (hasEmptySlot()) {
addNewItem(*item.clone());
return true;
[Code] ....
Also I was wondering, is there some sort of built-in cloning functionality or do I have to write the clone functions myself? When creating new instances I see that I can either pass the constructor properties or a reference to an object of the same type.
For instance:
Code:
new InventoryItem(index, name....);
new InventoryItem(const InventoryItem&);
Is the second one casting?
Each of my header includes is protected by directives. I think I don't have to include Boolean in my work space because it is already included in the external dependencies section. and the Boolean.h is in the include path.
MachineShop, Boolean etc got undeclared identifier error
Tried to comment out the directives, to no avail.
Code:
#include <iostream>
#include <string.h>
#ifndef BOOLEAN_H_
# include "Boolean.h"
#endif
#ifndef PROCESS_H_
# include "Process.h"
#endif
#ifndef MACHINESHOP_H_
[Code] ....