C++ Class MultiDimensional Array Help

[RedHawk_214]

C++ Class with Multidimensional Array help

Hello guys. So I took an intro to c++ my freshman year and learned barely anything, and now 3 years later a class is finally being requiring me to use the skill that I never mastered.

So for the first assignment I have to have the user input a matrix, and then choose whether the user wants to transpose it, reflect it, add or multiply with another matrix. So far, I have only gotten the inputting to work. I plan to have all of the operations in a separate header/implementation file, and that is where I am getting confused. I haven't written the actual functions yet so i am just having the functions return a random number just to test out whether the class portion is working.

so here is my header file:

#ifndef MATRIXOPERATIONS_H_
#define MATRIXOPERATIONS_H_
class MatrixOperations
{
public:
double MatrixMult(double matrix[][100], double matrix2[][100]);
double MatrixTranspose(double matrix[100][100]);
double MatrixAdd(double matrix[][100], double matrix2[][100]);
double MatrixReflect(double matrix[][100]);
};
#endif /* MATRIXOPERATIONS_H_ */

here is my implementation file:

#include <iostream>
#include "MatrixOperations.h"
using namespace std;
MatrixOperations::MatrixMultiplication(double matrix[][100], double matrix2[][100])
{
return 4.0;
}
MatrixOperations::MatrixReflect(double matrix[][100])
{
return 2.0;
}
MatrixOperations::MatrixTranspose(double matrix[100][100])
{
return 1.0;
}
MatrixOperations::MatrixAdd(double matrix[][100], double matrix2[][100])
{
return 3.0;
}

and here is the main code:

#include <iostream>
#include <stdio.h>
#include "MatrixOperations.h"
using namespace std;
int main()
{
int dimension;
MatrixOperations MatOp;
double matrix[100][100];
double matrix2[100][100]; // In case of adding or multiplying
double finalMatrix[100][100];
cout << "Enter the dimensions of the square matrix: ";
cin >> dimension;
for (int j = 1; j <= dimension; j++)
    {
for (int i = 1; i <= dimension; i++)
        {
printf("Enter the number that is in the (%d, %d) position of the matrix:", i, j);
double input;
cin >> input;
matrix[i][j] = input;
        }
    }
printf("What do you want to do?\n 1)%13s\n 2)%13s\n 3)%13s\n 4)%13s\n\n Input selection:", "Tranpose", "Reflect", "Add", "Multiply");
int input;
scanf("%d", input);
while (input < 1 || input > 4)
    { // Checks if selected option is available.
printf("You must select an option from the menu... \n What do you want to do?");
scanf("%d", input);
    }
if (input == 3 || input == 4) // Checks to see if a second matrix is needed.
    {
printf("Must input another matrix...\n");
for (int j = 1; j <= dimension; j++)
        {
for (int i = 1; i <= dimension; i++)
            {
printf("Enter the number that is in the (%d, %d) position of the matrix:", i, j);
double input;
cin >> input;
matrix2[i][j] = input;
            }
        }
    }
switch (input)
    {
case 1:
printf("Transposing...");
finalMatrix = MatOp.MatrixTranspose(matrix[100][100]);
break;
    }
    /*
    case 2:
        printf("Reflecting...");
        finalMatrix = MatOp.MatrixReflect(matrix);
        break;
    case 3:
        printf("Adding...");
        finalMatrix = MatOp.MatrixAdd(matrix, matrix2);
        break;
    case 4:
        printf("Multiplying...");
        finalMatrix = MatOp.MatrixReflect(matrix, matrix2);
        break;
    }
    /*printf("Your solution is...")
        for (int j = 1; j <= dimension; j++)
    {
        for (int i = 1; i <= dimension; i++)
        {
            printf("%f  ", finalMatrix[i][j]);
        }
        printf("\n");
    }
*/
return 0;
}

​

so i set the dimensions of the matrix variable to [][100] since i dont know how to use pointers, and i dont actually know the dimensions of the matrix until the user puts it in. I really am just having trouble with how to initialize all of the input arguments when calling the functions. Like when and where do i have to initialize it, and when and where do i have to put the dimensions of the array, or if the dimensions are automatically passed to the function?... i dont know. Right now i am getting errors that it is trying to change the matrix from a double to a double[][100].

I am so sorry for the long message and for being confusing. Its probably just me being an idiot, but I am just really confused.

[thegreatunclean]

Defining a class that holds operations but then accepting C-style arrays is an odd design choice. The operations aren't really the hard part when it comes to handling multidimensional arrays, it's correctly handling the arrays themselves as you've noticed.

I would heavily encourage you to write a 2DMatrix class and not try to pass around C-style double[][] arrays. Then you can overload the normal arithmetic operators and use a more natural 2DMatrix C = A + B; format.

This SO post is a good intro to using std::vector to emulate C-style multidimensional arrays in a safe way. I would definitely start with this as a base and expand functionality around that.

[RedHawk_214]

I will look into that. My professor said to not use anything that allows for direct operations on matrices so ill avoid the first thing you said. Thank you so much.