How can I print the result of add function..? - c++

Question

I want to pass the result object to another display function,but for some reason its not working. cmd stops working
I tried using different aproaches but none seems to be working..
Basically I ahbe to add two matrices using a function and return type should be of an object. I want to print the result of this addition, not in this function but using another function.
#include<iostream>
using namespace::std;
class Matrix{
private:
int row,column; //dimensions row x column
int **matrix; //pointer to a pointer to int
void allocarray(){ //method to llocate array matrix and the matrix[i] arrays
matrix=new int*[row];
for(int i=0;i<row;i++){
matrix[i]=new int[column];
}
}
public:
Matrix(int rowsize, int columnsize); //default constructor
Matrix(); //user defined constructor
~Matrix(); //destructor
void input();
Matrix Add(Matrix);
void display(Matrix);
};
Matrix Matrix::Add(Matrix m2)
{
Matrix result(3,3);
for(int i=0;i<row;i++)
{
for( int j=0;j<column;j++)
{
result.matrix[i][j]=this->matrix[i][j]+m2.matrix[i][j];
}
}
return *this;
}
void Matrix::display(Matrix m)
{
for(int i=0;i<row;i++)
{
for( int j=0;j<column;j++)
{
cout<<m.matrix[i][j];
}
cout<<endl;
}
}
Matrix::Matrix( int rowsize, int columnsize):row(rowsize),column(columnsize) //dynamivally allocate
{
allocarray();
for(int i=0;i<row;i++)
{
for( int j=0;j<column;j++)
{
matrix[i][j]=0; //initilze all values to 0
}
}
}
Matrix::~Matrix() //destructor
{
for( int i=0;i<row;i++)
{
delete [] matrix[i];
}
delete [] matrix;
}
void Matrix::input()
{
cout<<"enter the elements for the matrix"<<endl;
for(int i=0;i<row;i++)
{
for(int j=0;j<column;j++)
cin>>matrix[i][j];
cout<<"\n"; //check it after performing functions!
}
}
int main()
{
Matrix obj1(3,3),obj2(3,3),res(3,3);
cout<<"enter elements for matrix one";
obj1.input();
cout<<"enter elements for matrix two";
obj2.input();
cout<<"addition of two matrices";
res=obj1.Add(obj2);
obj1.display(res);
return 0;
}
so here's the code for copy constructor
Matrix::Matrix(const Matrix &m):row(m.row),column(m.column)
{
allocarray();
for(int i=0;i<row<i++)
{
for(int j=0;j<column;j++)
{
matrix[i][j]=m.matrix[i][j];
}
}
}

Answer 1

Your class doesn't define a copy constructor or an assignment operator. But any attempt to pass a matrix to a function or return a matrix from a function copies the matrix. Your code fails because the destructor is freeing memory that is still in use. When writing classes that manually manage memory you must follow the rule of three. Do this and your program will work.
Also as Patato said you need to add return result; to Matrix::Add, but that will also fail unless you follow the rule of three.
EDIT: changed the link to point to the Stack Overflow page on the rule of three, which is much more helpful than the Wikipedia page.
EDIT: here's an example copy constructor for this class, it's fairly similar to the regular constructor
Matrix::Matrix(const Matrix& rhs):row(rhs.row),column(rhs.column)
{
allocarray();
for(int i=0;i<row;i++)
{
for( int j=0;j<column;j++)
{
matrix[i][j]=rhs.matrix[i][j];
}
}
}

Answer 2

using reference is good, and your add function does not return the add result
so it looks like this
Matrix Matrix::Add(Matrix &m2)
{
Matrix result(3,3);
for(int i=0;i<row;i++)
{
for( int j=0;j<column;j++)
{
result.matrix[i][j]=this->matrix[i][j]+m2.matrix[i][j];
}
}
return result;
}
but it is still not very good, after this function the result will be deleted

Answer 3

You could either pass a reference to the function (and return one too):
Matrix& Add(Matrix&);
or write a copy constructor, so that you can use the actual matrix later.
Also, you shouldn't be returning the matrix you're adding to, but the result:
Matrix& Matrix::Add(Matrix &m2)
{
Matrix *result = new Matrix(3,3);
for(int i=0;i<row;i++)
{
for( int j=0;j<column;j++)
{
result->matrix[i][j]=this->matrix[i][j]+m2.matrix[i][j];
}
}
return *result;
}