Matrix mult help (pointers)

[toomanystars]

Hi guys,

Having an issue with matrix multiplication. For the final matrix, I get the proper size for example A[d][e] * B[x][y]= C[d][y].

I also know the algorithm is correct (I found similar ones online) but the damn program keeps crashing, and I have been at it for some time.

Everything else in the program works fine, for example addition, subtraction, copy constructor etc.

Thanks,

Mike

class Matrix{
public:
	Matrix(){}
	Matrix(int a, int b):row(a),col(b){
		int i;
		pointer=new int*[row];
		for(i=0;i<row;i++)
			pointer[i]=new int[col];
	}
	Matrix(Matrix& m){
		row=m.row;
		col=m.col;
		int i,j;
		pointer=new int*[row];
		for(i=0;i<row;i++)
			pointer[i]=new int[col];

		for(i=0;i<row;i++)
			for(j=0;j<col;j++)
				pointer[i][j]=m.pointer[i][j];
	}
	Matrix operator=(Matrix& m){
		row=m.row;
		col=m.col;
		int i, j;
		pointer=new int*[row];
		for(i=0;i<row;i++)
			pointer[i]=new int[col];
		for(i=0;i<row;i++)
			for(j=0;j<col;j++)
				pointer[i][j]=m.pointer[i][j];
		return *this;
	}
	Matrix operator*(Matrix& m){
		Matrix solution;
		solution.row=row;
		solution.col=m.col;
	
		cout<<"-------------------------\n";
		cout<<"M1\n";
		cout<<"row: "<<row<<endl;
		cout<<"col: "<<col<<endl;
		cout<<"+++++++++++++++++++++++++\n";

		cout<<"M2\n";
		cout<<"row: "<<m.row<<endl;
		cout<<"col: "<<m.col<<endl;

		cout<<"+++++++++++++++++++++++++\n";
		cout<<"Final row: "<<solution.row<<endl;//good
		cout<<"Final col: "<<solution.col<<endl;//good

		int i,j,k;
		solution.pointer=new int*[solution.row]();//initialized to zero
		for(i=0;i<solution.row;i++)
			solution.pointer[i]=new int[solution.col]();//initialized to zero

		


		for(i=0;i<row;i++){
			for(j=0;j<m.col;j++){
				for(k=0;k<col;k++){
					solution.pointer[i][j]+=m.pointer[i][k]*pointer[k][j];////PROBLME HERE ON THIS LINE!!!!!!!!!!!!!!!!
				}
			}
		}
			
		
		return solution;
	}
	Matrix operator-(Matrix& m){
		Matrix solution;
		solution.row=row;
		solution.col=col;
		
		int i,j;
		solution.pointer=new int*[solution.row];
		for(i=0;i<solution.row;i++)
			solution.pointer[i]=new int[solution.col];
		for(i=0;i<solution.row;i++)
			for(j=0;j<solution.col;j++)
				solution.pointer[i][j]=m.pointer[i][j]-pointer[i][j];
		return solution;
	}
	bool check_legality(Matrix& m){
		if(m.row==row && m.col==col)return true;
		else
			return false;
	}
	Matrix operator+(Matrix& m){
		Matrix solution;
		int i, j;
		solution.row=m.row;
		solution.col=m.col;
		solution.pointer=new int*[solution.row];
		for(i=0;i<solution.row;i++)
			solution.pointer[i]=new int[solution.col];
		for(i=0;i<solution.row;i++)
			for(j=0;j<solution.col;j++)
				solution.pointer[i][j]=m.pointer[i][j]+pointer[i][j];
		return solution;
	}
	~Matrix(){
		for(int i=0;i<row;i++)
			delete[]pointer[i];
		delete[] pointer;
	}   
	friend istream& operator>>(istream& in, Matrix& m);
	friend ostream& operator<<(ostream& out, Matrix& m);
private:
	int **pointer;
	int row, col;
}; 


int main(){

	
	Matrix m1(4,2), m2(2,4);

	cin>>m1;
	cout<<endl<<m1<<endl;

	cin>>m2;
	cout<<endl<<m2<<endl;
	
	Matrix mult=m2*m1;

	cout<<mult;
	
	_getch();
	return 0;
}	
ostream& operator<<(ostream& out, Matrix& m){
	for(int i=0;i<m.row;i++){
		for(int j=0;j<m.col;j++){
			out<<m.pointer[i][j]<<" ";
		}
		out<<endl;
	}
	cout<<endl;
	return out;
}
istream& operator>>(istream& in, Matrix& m){
	for(int i=0;i<m.row;i++){
		for(int j=0;j<m.col;j++){
			cout<<"Enter "<<"["<<i<<"]["<<j<<"]"<<" value: ";
			in>>m.pointer[i][j];
		}
	}
	return in;
}

[ToniAz]

Crashing when working with arrays is mostly due to two reasons: accessing restricted memory cells and memory leakage (I'm not 100% if the terms are technically correct).

You only used delete in the destructor, what about the functions that return a matrix? Don't you want to delete your temporary matrix?

[toomanystars]

Addition and subtractions work without the delete, I would imagine that multiplication should work the same way. I also don't recall reading in the book I am going through right now anything about having to delete anything from each overloaded function.

[ToniAz]

You're right I wanted to ask whether addition and subtraction crashed your application. Anyway the algorithm seems right, and I even tried rewriting the multiplication manually inside main and without using classes, there was no problem.

Also, I don't get how you're assuming values are initialized to 0. And, how didn't this give you compile errors?
Matrix operator=(Matrix& m)

It should be like this

Matrix & operator=(const Matrix& m)

[toomanystars]

Does multiplication work for you only inside main? How about the function?

Mike

[ToniAz]

Okay, I've been testing for the last hour now :D

I fixed something:

for(i=0;i<solution.row;i++){
		for(j=0;j<solution.col;j++){
			for(k=0;k<m.row;k++){
					solution.pointer[i][j]+=pointer[i][k] * m.pointer[k][j];////PROBLME HERE ON THIS LINE!!!!!!!!!!!!!!!!
                    cout << "!" << pointer[i][k] << " " << m.pointer[k][j] <<
                    endl;

And I make sure the multiplication operator returns correctly. For some reason, there seems to be a whooole lot of integers in the io buffer that come up all at once when using any cout... Couldn't figure out why, and I probably won't because I never use the new[] operator...

If your only interested in the algorithm itself rather than practicing C++ dynamic arrays, go ahead and use vector in STL.

[toomanystars]

Thanks a lot for the help. I was looking however to returning the object, but what you suggest should be fine for now. I think with a little more experience, I will come back to this and try to figure it out again.

Mike