Earless - 1 month ago 4x

C++ Question

im trying to write a program in C++ which is able to multiply matrices.

Unfortunately, I'm not able to create a matrice out of 2 vectors. The goal: I typ in the number of rows and the number of coloms. Then there should be a matrix created with those dimensions. Then I can fill (for example rows = 2 cols = 2 => Matrix = 2 x 2) the matrix by typing in the numbers. I tried it with this 2 codes: (second one is in a header file)

`#include <iostream>`

#include "Matrix_functions.hpp"

using namespace std;

int main ()

{

//matrices and dimensions

int rows1, cols1, rows2, cols2;

int **matrix1, **matrix2, **result = 0;

cout << "Enter matrix dimensions" << "\n" << endl;

cin >> rows1 >> cols1 >> rows2 >> cols2;

cout << "Enter a matrix" << "\n" << endl;

matrix1 = new int*[rows1];

matrix2 = new int*[rows2];

// Read values from the command line into a matrix

read_matrix(matrix1, rows1, cols1);

read_matrix(matrix2, rows2, cols2);

// Multiply matrix1 one and matrix2, and put the result in matrix result

//multiply_matrix(matrix1, rows1, cols1, matrix2, rows2, cols2, result);

//print_matrix(result, rows1, cols2);

//TODO: free memory holding the matrices

return 0;

}

This is the main code. Now the header file with the read_matrix function:

`#ifndef MATRIX_FUNCTIONS_H_INCLUDED`

#define MATRIX_FUNCTIONS_H_INCLUDED

void read_matrix(int** matrix, int rows, int cols)

{

for(int i = 0; i < rows; ++i)

matrix[i] = new int[cols];

}

//int print_matrix(int result, int rows1, int cols1)

//{

// return 0;

//}

//int multiply_matrix(int matrix2, int rows2, int cols2, int matrix3, int rows3, int cols3, int result2)

//{

// return result2;

//}

#endif // MATRIX_FUNCTIONS_H_INCLUDED

The first part works. I can fill in the dimensions. But then it prints: Enter a matrix, and the program quits. Why am I not able to fill in the numbers of the matrix?

I hope someone is able to help me. If there are things unclear, let me know.

Thanks in advance:D

(dont pay attention to most of the comments; those are for the rest of the multiplying code)

Answer

You forgot to `cin`

the numbers, try this:

```
void read_matrix(int** matrix, int rows, int cols)
{
for(int i = 0; i < rows; ++i) {
matrix[i] = new int[cols];
for(int j = 0; i < cols; ++i) {
cin >> matrix[i][j];
}
}
}
```

Source (Stackoverflow)

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