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I am trying to create a four-dimensional array of pointers. The type of the array is a Gurobi type "GRBVar". However, I am unsure of the syntax to use.
GRBVar**** testArray = new GRBVar*** [numBuses];
for (int i = 0; i < numBuses; i++) {
testArray[i] = new GRBVar** [maxRoute];
for (int j = 0; j < maxRoute; j++) {
testArray[j] = new GRBVar* [numJobs];
for (int k = 0; k < numJobs; k++) {
testArray[k] = new GRBVar[numJobs];
}
}
}
The above causes an error. How can I fix it?
Literally you can create it like GRBVar* array[10][10][10][10], but it's better to use nested std::vector for this purpose, like std::vector<GRBVar*>, std::vector<std::vector<GRBVar*>> etc, and moreover - use aliases, like
using Jobs = std::vector<GRBVar*>;
using Routes = std::vector<Jobs>;
using Buses = std::vector<Routes>;
And then initialize it:
Buses buses;
for (int i = 0; i < numBuses; i++) {
Routes routes;
for (int j = 0; j < maxRoute; j++) {
Jobs jobs;
for (int k = 0; k < numJobs; k++) {
jobs.push_nack(new GRBVar);
}
routes.push_back(jobs);
}
buses.push_back(routes);
}
You need to increase the [] levels in your nested for loops to assign the pointers to their proper objects.
#include <iostream>
typedef struct SomeObject { int r; } *GRBVar; // this keeps the syntax as close as possible to the original question
int main()
{
int numBuses = 2;
int maxRoute = 3;
int numJobs = 4;
SomeObject* someobjects = new SomeObject[numBuses * maxRoute * numJobs * numJobs];
// This creates and initializes a 4D array of pointers to SomeObjects
GRBVar**** testArray = new GRBVar ***[numBuses];
for (int i = 0; i < numBuses; i++) {
testArray[i] = new GRBVar **[maxRoute];
for (int j = 0; j < maxRoute; j++) {
testArray[i][j] = new GRBVar *[numJobs];
for (int k = 0; k < numJobs; k++) {
testArray[i][j][k] = new GRBVar[numJobs];
for (int m = 0; m < numJobs; m++)
testArray[i][j][k][m] = someobjects++;
}
}
}
testArray[0][0][0][0]->r = 1;
testArray[0][0][0][1]->r = 2;
testArray[0][0][1][0]->r = 3;
std::cout << testArray[0][0][0][0]->r << " " << testArray[0][0][0][1]->r << " " << testArray[0][0][1][0]->r << "\n";
}
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when I trying to implement the counting sort I got this error " the problem caused the program to stop working correctly Windows will close the program and notify you if a solution is available "
void CountingSort(int *A,int size) {
int SizeC = Max(A, size);
int* B = new int[size];
int* C = new int[SizeC+1];
for (int i = 0; i < SizeC; i++) {
C[i] = 0;
}
for (int i = 0; i < size; i++) {
C[A[i]]++ ;
}
for (int i = 0; i <SizeC; i++)
{
C[i] += C[i - 1];
}
for (int j = size - 1; j >= 0; j--) {
B[C[A[j]]] = A[j];
C[A[j]] --;
}
for (int i = 0; i < size; i++) {
cout << B[i] << "\t" << endl;
}
delete[] C;
delete[] B;
}
this is the error
i < SizeC and i <SizeC should be i <= SizeC. Otherwise, the elements with value SizeC won't be treated properly.
C[i] += C[i - 1]; with i = 0 will result in out-of-range read of C[-1]. The initialization of corresponding for loop should be int i = 1, not int i = 0.
The decrementing C[A[j]] --; should happen before B[C[A[j]]] = A[j];, or out-of-range write of B[size] will happen.
This program won't work well when the array A contains negative values.
Fixed code (negative values are still not supported):
void CountingSort(int *A,int size) {
int SizeC = Max(A, size);
int* B = new int[size];
int* C = new int[SizeC+1];
for (int i = 0; i <= SizeC; i++) {
C[i] = 0;
}
for (int i = 0; i < size; i++) {
C[A[i]]++ ;
}
for (int i = 1; i <= SizeC; i++)
{
C[i] += C[i - 1];
}
for (int j = size - 1; j >= 0; j--) {
C[A[j]] --;
B[C[A[j]]] = A[j];
}
for (int i = 0; i < size; i++) {
cout << B[i] << "\t" << endl;
}
delete[] C;
delete[] B;
}
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So I need help. The problem is that an int arr[5] = {0};
I know the array has the values {0,0,0,0,0} filling the whole array. At the end of the code the array must have the values {1,2,3,4,5} inside it. To solve it must use a nested for loop.
I have tried the following code
Sorry if there is an error in the way this question is formatted this is my first time and using mobile.
int arr[5] = {0};
for(int j = 1; j<6; j++)
{
for(int i = 0; i<5; i++)
{
arr[i] = j;
}
}
I don't know what the benefit of that but If you have to use nested for loop, the following is an option
int main()
{
int arr[5] = {0};
for(int j = 0; j < 5; ++j)
{
for(int i = 1; i < 2; ++i)
{
arr[j] = j+i;
}
}
for(int i{};i<5;++i) std::cout << arr[i] << ", ";
}
Or like #JaMit comment suggests
int main()
{
int arr[5] = {0};
for(int j = 0; j < 5; ++j)
{
for(int i = 0; i < j+1; ++i)
{
arr[j]++;
}
}
for(int i{};i<5;++i) std::cout << arr[i] << ", ";
}
I'm guessing your professor means you should generate the final results using only incrementation. In other words, I'm guessing you're not allowed to assign values after the int arr[5] = {0}; line (so an expression like arr[i] = j; is not allowed).
In that case, you could solve the problem as follows:
int arr[5] = {0};
for (int i = 0; i < 5; i++) {
for (int j = i; j < 5; j++) {
arr[j]++;
}
}
Now we have only used incrementation and the final result is {1, 2, 3, 4, 5}.
I'm currently reading Jumping into C++ by Alex Allain and am stuck on Chapter 14's Practice Problem number 1.
Write a function that builds a two-dimensional multiplication table with arbitrary sizes for two dimensions.
I'm having trouble actually assigning the times table to the array but all these nested loops are giving me a headache! I'm getting an output of "999999999".
My Code:
#include <iostream>
using namespace std;
int main()
{
int **p_p_tictactoe;
p_p_tictactoe = new int*[3];
for (int i = 0; i < 3; i++)
p_p_tictactoe[i] = new int[3];
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < 3; j++)
{
p_p_tictactoe[i][j] = 1;
for (int y = 0; y < 4; y++)
{
for (int t = 0; t < 4; t++)
{
p_p_tictactoe[i][j] = y * t;
}
}
cout << p_p_tictactoe[i][j];
}
}
cin.get();
for (int i = 0; i < 3; i++)
delete[] p_p_tictactoe[i];
delete[] p_p_tictactoe;
}
I am trying to create a 2d array pointer with my own class, Tile, as type. I have looked at the code example at How do I declare a 2d array in C++ using new?. The following code works perfectly:
int** ary = new int*[sizeX];
for(int i = 0; i < sizeX; ++i)
ary[i] = new int[sizeY];
for(int i = 0; i < 8; i++)
for(int j = 0; j < 8; j++)
ary[i][j] = 5;
for(int i = 0; i < 8; i++)
for(int j = 0; j < 8; j++)
cout << ary[i][j];
However when I try to change type from int to my own class, Tile, I get an
No viable overloaded '='
error in XCode, and I can't figure out what this means. I use the following code:
Tile** t;
t = new Tile*[8];
for(int i = 0; i < 8; ++i)
t[i] = new Tile[8];
for(int i = 0; i < 8; i++) {
for(int j = 0; j < 8; j++) {
t[i][j] = new Tile(new NoPiece());
}
}
for(int i = 0; i < 8; i++) {
for(int j = 0; j < 8; j++) {
cout << (t[i][j].get_piece()).to_string();
}
}
Here is the code for Tile.cpp:
#include "Tile.h"
Tile::Tile() {
}
Tile::Tile(Piece p) {
piece = &p;
}
Piece Tile::get_piece() {
return *piece;
}
And the code for Tile.h:
#include <iostream>
#include "Piece.h"
class Tile {
Piece * piece;
public:
Tile();
Tile(Piece p);
Piece get_piece();
};
The difference between two code snippets is that the one using int treats array elements like values, i.e. assigns
ary[i][j] = 5;
while the one using Tile treats array elements like pointers:
t[i][j] = new Tile(new NoPiece()); // new makes a pointer to Tile
Change the assignment to one without new to fix the problem:
t[i][j] = Tile(new NoPiece());
There is nothing wrong to making a 2D array of pointers, too - all you need is to declare it as a "triple pointer", and add an extra level of indirection:
Tile*** t;
t = new Tile**[8];
for(int i = 0; i < 8; ++i)
t[i] = new Tile*[8];
for(int i = 0; i < 8; i++) {
for(int j = 0; j < 8; j++) {
t[i][j] = new Tile(new NoPiece());
}
}
for(int i = 0; i < 8; i++) {
for(int j = 0; j < 8; j++) {
cout << (t[i][j]->get_piece()).to_string();
}
}
// Don't forget to free the tiles and the array
for(int i = 0; i < 8; i++) {
for(int j = 0; j < 8; j++) {
delete t[i][j];
}
delete[] t[i];
}
I have this function meant to initialize a multidimensional 2d (6x6) array to zero. I call the function in main using cout to test it and it outputs garbage. Please help. Thanks!
int** initializeArray(void)
{
typedef int* rollArray; //this line is actually outside of the function in my
//program
int i, j;
rollArray *m = new rollArray[6];
for (i = 0; i < 6; i++)
m[i] = new int[6];
for (i = 0; i < 6; i++)
for (j = 0; j < 6; j++)
m[i][j] = 0;
return m;
}
If the value 6 is known at compile-time, I would suggest using std::array in a nested fashion. For example:
#include <array>
#include <iostream>
int main()
{
std::array<std::array<int,6>,6> a = {0};
for (int i = 0; i < 6; ++i)
{
for (int j = 0; j < 6; ++j)
{
std::cout << a[i][j] << std::endl; // Prints 0.
}
}
return 0;
}
In fact, you won't even need to create a function to initialize your array. Declare your nested array and you are good to go. (If you don't know the dimension at compile-time, you could use std::vector in a similar fashion.)
The problem is with your test.
How can you mess up such a simple test? Just use:
int ** a = initializeArray();
int i,j;
for (i = 0; i < 6; i++) {
for (j = 0; j < 6; j++) {
cout << a[i][j] << " ";
}
cout << endl;
}