Hey I am beginner at C++ programming. I have made a program that is meant to add two 2D arrays together. However, The program outputs the values until the program crashes. Can someone help me to identify the problem?
#include <iostream>
using namespace std;
int main(int argc, char** argv)
{
int a[10][10], c[10][10], i, j;
for (i = 1; i <= 10; ++i)
{
for(j=0; j < 10; ++j)
{
a[i][j] = i * j;
}
}
// We are able to treat the individual columns as arrays
for (int i = 0; i < 10; ++i)
{
int *b = a[i];
for (int j = 0; j < 10; ++j)
{
cout << b[j] << " ";
}
cout << endl;
}
cout << "****" << endl;
// Declare a multidimensional array on the heap
int **b = new int*[10];
// need to allocate all members individually
for (int i = 0; i < 10; ++i)
{
b[i] = new int[10];
}
// Set the values of b
for (int i = 0; i < 10; ++i)
{
for (j = 0; j < 10; ++j)
{
b[i][j] = (i * 10) + j;
}
}
for (i = 0; i < 10; ++i)
{
for (j = 1; j <= 10; ++j)
{
c[i][j] = a[i][j] + b[i][j];
}
}
for (i = 0; i < 10; ++i)
{
for (j = 1; j <= 10; ++j)
{
cout << c[i][j] << endl;
}
}
// Delete the multidimensional array - have to delete each part
for (int i = 0; i < 10; ++i)
{
delete[] b[i];
}
delete[] b;
return 0;
}
I corrected your code.Now, It's working and program didn't crash. You can try it out.
#include<conio.h>
#include<iostream.h>
int main(int argc, char** argv)
{
int a[10][10], c[10][10], i, j;
for (i = 0; i <10; ++i)
{
for(j=0; j < 10; ++j)
{
a[i][j] = i * j;
}
}
//We are able to treat the individual columns as arrays;
for (i = 0; i < 10; ++i)
{
int *b = a[i];
for (int j = 0; j < 10; ++j)
{
cout << b[j] << " ";
}
cout << endl;
}
cout << "****" << endl;
//Declare a multidimensional array on the heap;
int **b = new int*[10];
//need to allocate all members individually
for (i = 0; i < 10; ++i)
{
b[i] = new int[10];
}
//Set the values of b
for ( i = 0; i < 10; ++i)
{
for (j = 0; j < 10; ++j)
{
b[i][j] = (i * 10) + j;
}
}
for (i = 0; i < 10; ++i)
{
for (j = 0; j <10; ++j)
{
c[i][j] = a[i][j] + b[i][j];
}
}
for (i = 0; i < 10; ++i)
{
for (j = 0;j < 10; ++j)
{
cout << c[i][j] << " ";
}
cout<<endl;
}
// Delete the multidimensional array - have to delete each part
for (i = 0; i < 10; ++i)
{
delete[] b[i];
}
delete[] b;
return 0;
}
Related
Here is my driver
int square[2][2] = {
{1,2},
{3,4}
};
matrixMulti(square, 2);
Here is my function
void matrixMulti(const int a[][2], const int rows) {
int b[2][2];
for (int i = 0; i < 2; i++) {
for (int j = 0; j < 2; j++) {
for (int k = 0; k < 2; k++) {
b[i][j] += a[i][k] * a[k][j];
}
}
}
cout << "new matrix " << endl;
for (int i = 0; i < 2; i++) {
for (int j = 0; j < 2; j++) {
cout << b[i][j] << " ";
}
cout << endl;
}
}
The output is:
new matrix
-858993453 -858993450
-858993445 -858993438
I am confused as to why it is printing the memory addresses rather then the values stored in them and what can be done to get it to print the values rather than the memory address.
You wrote:
int b[2][2];
and then
b[i][j] += ...
Where did you initialize b ?
int b[2][2] = {};
or
int b[2][2] = {0,0};
Should do the job.
Garbage values are being printed, not the address of the array.
Here is why.
In this snippet of code
void matrixMulti(const int a[][2], const int rows) {
int b[2][2];
for (int i = 0; i < 2; i++) {
for (int j = 0; j < 2; j++) {
for (int k = 0; k < 2; k++) {
b[i][j] += a[i][k] * a[k][j];
}
}
}
You allocated space for int b[2][2], but you do not initialize it to a value. This would be fine except in the for-loop body.
b[i][j] += a[i][k] * a[k][j]; <=> b[i][j] = b[i][j] + a[i][k] * a[k][j];
you are referencing the value of b[i][j] before it is initialized. In other words you say b[i][j] is equal to b[i][j] + a[i][k] * a[k][j], but you can't do this as, the value of b[i][j] is unknown.
The solution to this is to initialize int b[2][2] = {{0,0},{0,0}};
I am trying to write a function in C++ that multiplies two matrices A, B which have been dynamically allocated. I am currently trying to get the multiplication code working, then I will attempt to turn it into a function. Right now I am getting an error of sorts; "segmentation fault (core dumped)". I have narrowed it down to the multiplication part of my code but I have no idea what is wrong with it. Can someone help me please? My code is shown below.
#include <iostream>
#include <cassert>
int main()
{
int rowsA = 5; // number of rows
int colsA= 3; // number of coloumns
// dynamically allocating A
double** A;
A = new double* [rowsA];
A[0] = new double [rowsA*colsA];
for (int i = 1; i < rowsA; i++)
{
A[i] = A[i-1] + colsA;
}
// Storing elements of matrix A
for(int i = 0; i < rowsA; ++i)
{
for(int j = 0; j < colsA; ++j)
{
std::cout << "Enter element A" << i + 1 << j + 1 << " : ";
std::cin >> A[i][j];
}
}
int rowsB = 3; // number of rows
int colsB = 5; // number of coloumns
// dynamically allocating B
double** B;
B = new double* [rowsB];
B[0] = new double [rowsB*colsB];
for (int i = 1; i < rowsB; i++)
{
B[i] = B[i-1] + colsB;
}
// Storing elements of matrix B
for(int i = 0; i < rowsB; ++i)
{
for(int j = 0; j < colsB; ++j)
{
std::cout << "Enter element B" << i + 1 << j + 1 << " : ";
std::cin >> B[i][j];
}
}
// checking matrix multiplication qualification
assert(colsA == rowsB);
// dynamically allocating C
double** C;
C = new double* [rowsA];
C[0] = new double [rowsA*colsB];
for (int i = 1; i < rowsA; i++)
{
C[i] = C[i-1] + colsB;
}
// Initializing elements of matrix C to 0
for(int i = 0; i < rowsA; ++i)
{
for(int j = 0; j < colsB; ++j)
{
C[i][j]=0;
}
}
// multiplication
for(int i = 0; i < rowsA; ++i)
{
for(int j = 0; j < colsB; ++j)
{
for(int k = 0; k < colsB; ++k)
{
C[i][j] += A[i][k] * B[k][j];
}
}
}
// Displaying the multiplication of matrices A, B
std::cout<< "Matrix C: " << std::endl;
for(int i = 0; i < rowsA; ++i)
{
for(int j = 0; j < colsB; ++j)
{
std::cout << " " << C[i][j];
if(j == colsB-1)
{
std::cout << std::endl;
}
}
}
// deallocation
delete[] C[0];
delete[] C;
delete[] B[0];
delete[] B;
delete[] A[0];
delete[] A;
}
First, you say you are allocating the matrix properly but I'm not seeing any proof of that. You are allocating an array of pointers and only initializing the first index.. A[0] for example. This is incorrect. You need to allocate EACH ROW.
You have:
double** A;
A = new double* [rowsA];
A[0] = new double [rowsA*colsA]; //Incorrect. You only allocated A[0].
You need to allocate A[0] through A[rowsA - 1]..
Next, your multiplication loop (the inner most loop) is incorrect. It should be:
Iterate ColsA for that inner loop.
You have:
for(int i = 0; i < rowsA; ++i)
{
for(int j = 0; j < colsB; ++j)
{
for(int k = 0; k < colsB; ++k) //ColsB is incorrect. Should be colsA..
{
C[i][j] += A[i][k] * B[k][j]; //Segfaults here due to bad iteration..
}
}
}
The following would be correct:
#include <iostream>
#include <cassert>
double** create_matrix(int rows, int cols)
{
double** mat = new double* [rows]; //Allocate rows.
for (int i = 0; i < rows; ++i)
{
mat[i] = new double[cols](); //Allocate each row and zero initialize..
}
return mat;
}
void destroy_matrix(double** &mat, int rows)
{
if (mat)
{
for (int i = 0; i < rows; ++i)
{
delete[] mat[i]; //delete each row..
}
delete[] mat; //delete the rows..
mat = nullptr;
}
}
int main()
{
int rowsA = 5; // number of rows
int colsA= 3; // number of coloumns
double** matA = create_matrix(rowsA, colsA);
int rowsB = 3; // number of rows
int colsB = 5; // number of coloumns
double** matB = create_matrix(rowsB, colsB);
//Checking matrix multiplication qualification
assert(colsA == rowsB);
double** matC = create_matrix(rowsA, colsB);
//Multiplication
for(int i = 0; i < rowsA; ++i)
{
for(int j = 0; j < colsB; ++j)
{
for(int k = 0; k < colsA; ++k) //ColsA..
{
matC[i][j] += matA[i][k] * matB[k][j];
}
}
}
//Clean up..
destroy_matrix(matA, rowsA);
destroy_matrix(matB, rowsB);
destroy_matrix(matC, rowsA);
}
I am currently working on a program that prints a 5 variable truth table. I am using a 2d array. My code currently produces the table, but says it is corrupt and "the stack around the variable "table" was corrupted. Any help?
#include <iostream>
using namespace std;
int main() {
bool table[5][32];
for (int i = 0; i < 32; i++) {
for (int j = 0; j < 5; j++) {
table[i][j] = ((i >> j)& 1);
}
}
for (int i = 0; i < 32; i++) {
for (int j = 0; j < 5; j++) {
cout << table[i][j] << " ";
}
cout << endl;
}
return 0;
}
This is homework, so I would like to understand it, not just have an answer.
The index is wrong. Only table[0] to table[4] are available, so accessing table[5] to table[31] is illegal.
Try this:
#include <iostream>
using namespace std;
int main() {
bool table[32][5]; // swap 32 and 5
for (int i = 0; i < 32; i++) {
for (int j = 0; j < 5; j++) {
table[i][j] = ((i >> j)& 1);
}
}
for (int i = 0; i < 32; i++) {
for (int j = 0; j < 5; j++) {
cout << table[i][j] << " ";
}
cout << endl;
}
return 0;
}
There is attempt to read out of bound values from array.
If you need 5x32 matrix Use code below:
for (int i = 0; i < 5; i++) { // 32-> 5
for (int j = 0; j < 32; j++) { // 5->32
If you need 32x5 matrix then replace code below:
bool table[32][5]; //it was table[5][32];
I need to implement a 5x5 dynamic array where
every element in it is equal to the sum of its two indices. For example, the first element, at (0,0), has the value 0+0=0.
Here is my code:
# include<iostream>
using namespace std;
int main()
{
int size =5;
int *array=new int[size];
for (int i = 0; i < size; i++)
delete [] array;
return 0;
}
I need help to implement sum of index.
You need at first to implement a two-dimensional array.:)
Here you are.
#include <iostream>
int main()
{
const size_t N = 5;
int ( *array )[N] = new int[N][N];
for ( size_t i = 0; i < N; i++ )
{
for ( size_t j = 0; j < N; j++ ) array[i][j] = i + j;
}
for ( size_t i = 0; i < N; i++ )
{
for ( size_t j = 0; j < N; j++ ) std::cout << array[i][j] << ' ';
std::cout << std::endl;
}
delete [] array;
return 0;
}
And do not pay attention that the answer is down voted. There is nothing wrong with the answer. :)
Firstly, you should create a 2d-array, not just a array.
void foo() {
int **a = new int*[5];
for (int i = 0; i < 5; i++)
a[i] = new int[5];
}
for (int i = 0; i < 5; i++)
for (int j = 0; j < 5; j++)
a[i][j] = i + j;
for (int i = 0; i < 5; i++) {
for (int j = 0; j < 5; j++)
cout << a[i][j] << " ";
cout << endl;
}
for (int i = 0; i < 5; i++)
delete[] a[i];
delete[] a;
}
And, of course, don't forget to clear your memory)
I make a 3d dynamic array by this using this code
//layer = 2
//levelSize.x = 100
//levelSize.y = 100
level_array = new int**[layer];
for(int i = 0; i < layer; ++i)
{
level_array[i] = new int*[(int)levelSize.x];
for(int j = 0; j < levelSize.x; ++j)
level_array[i][j] = new int[(int)levelSize.y];
}
but when I want to delete it, the program crashes
for(int i = 0; i != levelSize.x; ++i)
{
for(int j = 0; j != levelSize.y; ++j)
{
delete[] level_array[i][j];
}
delete[] level_array[i];
}
delete[] level_array;
I don't know where is wrong in the code of deleting an array.
Please help me check the code, Thanks
You allocate memory for array with dimensions [layer][levelSize.x][levelSize.y], but while deleting you operate with it like with array with dimensions [levelSize.x][levelSize.y][somenting].
for(int i = 0; i != layer; ++i)
// ^^^^^ not levelSize.x
{
for(int j = 0; j != levelSize.x; ++j)
// ^^^^^^^^^^^ not levelSize.y
{
delete[] level_array[i][j];
}
delete[] level_array[i];
}
delete[] level_array;
Add this command to the end, otherwise the pointer will be at the top of the stack.
level_array = nullptr;
it's so important to make difference between deleting a single dim array and multi-dim allocated on the heap:
#include <iostream>
using std::cout;
using std::endl;
int main()
{
int*** ptrInt = new int**[3];
for(int i(0); i < 3; i++)
ptrInt[i] = new int*[3];
for(int i = 0; i < 3; i++)
{
for(int j(0); j < 3; j++)
ptrInt[i][j] = new int[3];
}
for(int i = 0; i < 3; i++)
{
for(int j(0); j < 3; j++)
for(int k(0); k < 3; k++)
ptrInt[i][j][k] = k;
}
for(int i = 0; i < 3; i++)
{
for(int j(0); j < 3; j++)
for(int k(0); k < 3; k++)
cout << "ptrInt[" << i << "][" << j << "][" << k << "]: " << ptrInt[i][j][k] << endl;
}
// now freeing memory:
for(int i = 0; i < 3; i++)
{
for(int j(0); j < 3; j++)
delete[] ptrInt[i][j];
delete[] ptrInt[i];
}
delete[] ptrInt;
cout << endl << endl << endl;
return 0;
}