Input to a dynamic multidimensional array

[tyler22]

Hi all,
I am currently reading Frank Luna's "Intro to 3D Game Programming".
One of the exercises is to write a program that calculates the transpose of a matrix. Following is the start of my code for this exercise:

#include <iostream>

using namespace std;

int main(void)
{
	cout << "-------------------------\n"
		<<"Transpose of a Matrix\n"
		<<  "-------------------------\n\n";

	int i,j; // i = rows; j = columns;

	cout << "Specify how many rows compose the matrix (up to 4): ";
	cin >> i;
	cout << "How many columns (up to 4): ";
	cin >> j;

	//declaration
	int ** matrix;
	//allocation
	matrix = new int*[i];
	for (int n = 0; n < i; n++)
	{
		matrix[n] = new int[j];
	}

	for (int a = 0; a < i; a++)
	{
		for (int b = 0; b < j; b++)
		{
			cout << "Enter " << a+1 << b+1 << ": ";
			cin >> matrix[i][j];
		}
	}
	return 0;
}

There is a problem with the way I am initializing the matrix array. I am not getting a compiler error, but the program crashes after you input the first value. Please tell me how to properly handle user input of the matrix elements.

Thanks,
tyler22

[tntxtnt]

line 32 should be cin >> matrix[a][b];. That's why you shouldn't name i = rows; j = columns;

and you must delete 2d array at the end of your program

[tyler22]

thanks tnt

[tyler22]

EDIT:
* I realized that the transpose of an mxn matrix is an nxm matrix. That explains why it worked fine for square matrices. I fixed the problem and the program works as expected now.*

I have another problem. I am not sure if I am deallocating the memory correctly or if the error is something else. Here is my new program:

#include <iostream>

using namespace std;

void printMatrix(int* arr[],int,int);
void transposeMatrix(int* arr[],int,int); //(matrix,rows,columns);

int main(void)
{
	cout << "-------------------------\n"
		<<"Transpose of a Matrix\n"
		<<  "-------------------------\n\n";

	int i,j; // i = rows; j = columns;

	cout << "Specify how many rows compose the matrix (up to 4): ";
	cin >> i;
	cout << "How many columns (up to 4): ";
	cin >> j;

	//declaration
	int ** matrix;
	//allocation
	matrix = new int*[i];
	for (int n = 0; n < i; n++)
	{
		matrix[n] = new int[j];
	}

	for (int a = 0; a < i; a++)
	{
		for (int b = 0; b < j; b++)
		{
			cout << "Enter " << a << b << ": ";
			cin >> matrix[a][b];
		}
	}
	
	cout << "A:\n";
	printMatrix(matrix,i,j);
	cout << "Transpose of A:\n";
	transposeMatrix(matrix,i,j);

	// deallocation
	for (int m = 0; m < i; m++)
		delete matrix[m];
	delete matrix;

	return 0;
}

void printMatrix(int* arr[],int i, int j)
{
	for (int a = 0; a < i; a++)
	{
		for (int b = 0; b < j; b++)
		{
			cout << arr[a][b] << " ";
		}
		cout << "\n";
	}
}

void transposeMatrix(int* arr[],int i,int j)
{
	//temporary array
	int ** temp;
	//allocation
	temp = new int*[i];
	for (int n = 0; n < i; n++)
	{
		temp[n] = new int[j];
	}

	for (int a = 0; a < i; a++)
	{
		for (int b = 0; b < j; b++)
		{
			temp[a][b] = arr[b][a]; //reverse
		}
	}

	printMatrix(temp,i,j);

	//deallocation
	for (int m = 0; m < i; m++)
		delete temp[m];
	delete temp;
}

For whatever reason, if I input a square matrix the program works as expected. Problems arise if I input matrices of different dimensions. For example, a 1x3 will crash when it tries to transpose, and a 4x2 will transpose part of the matrix correctly but the other elements will be crazy numbers (like -32777).

If anyone can help me I would appreciate it.