Thread: Matrix Class Operator Overloading.

Hello, I am making a matrix class with basic operations like addition, subtraction, Multiplication.
I have made a constructor that takes as input the rows and columns. I am done with
most of the functions but I am stuck with operator overloading.

Code:

#include <iostream>

using namespace std;

class Matrix
{
 int rows;
 int columns;
 int **matrix;
public:
 
 Matrix(int r, int c)
 {
	 rows = r;
     columns = c;
     matrix = new int *[rows];
     for (int i = 0; i < rows; i++)
    	matrix[i] = new int[columns];
 }

 int GetRows()
 {
	 return rows;
 }

 int GetColumns()
 {
	 return columns;
 }

 void IdentityMatrix()
 {
	 if (rows == columns)
	 {	
		 for (int i = 0; i < rows; i++)
			 for (int j = 0; j < columns; j++)
			 {
				 if ( i == j )
				 {
					 matrix[i][j]= 1;
				 }
				 else 
				 {
					 matrix[i][j]= 0;
				 }
			 }
	 }
	 else 
	 {
		 cout<<"Rows and Columns not equal, Can make identity Matrix";
	 }
 }

 void ZeroMatrix()
 {
	 for (int i = 0; i < rows; i++)
		 for (int j = 0; j < columns; j++)
			 matrix[i][j] = 0;
 }

 void DiagonalMatrix()
 {
	for (int i = 0; i < rows; i++)
		 for (int j = 0; j < columns; j++)
		 {
			 if ( i == j )
			 {
				continue;
			 }
			 else 
			 {
				 matrix[i][j]= 0;
			 }
		 }
 }

 void SetValues()
 {
	 for (int i = 0; i< rows; i++)
	   for (int j = 0; j< columns ;j++)
		   cin>>matrix[i][j];
 }

 int GetNumber(int i, int j)
 { 
	 return matrix[i][j];
 }

 void SetNumber(int i, int j , int number)
 { 
	 matrix[i][j] = number;
 }

 void ScalarMultiplication(int number)
 {
	 for (int i = 0; i< rows; i++)
	 {
		  for (int j = 0; j< columns ;j++)
		  {
			  matrix[i][j] = number*matrix[i][j];
		  }
	 }
 }

 Matrix operator + (Matrix &a, Matrix &b) I am getting error here, 
Like I know whenever I create the object, I will have to mention the rows and columns,
 But i cant figure out how here??     
 {
	 //if rows and coulmns of b are equal then 
	 //add them and store the result in result matrix
	 Matrix result;
	 for (int i = 0; i< rows; i++)
	 {
		  for (int j = 0; j< columns ;j++)
		  {
			  result[i][j] = a[i][j] + b[i][j];
		  }
	 }
	 return result;
 }

  void operator = (Matrix a, Matrix b)
 {
	 //if a and b are equal 
	 //then assign b to a
	
	 for (int i = 0; i< rows; i++)
	 {
		  for (int j = 0; j< columns ;j++)
		  {
			  a[i][j] = b[i][j];
		  }
	 }
	
 }


 void Print()
 {
	  for (int i = 0; i< rows; i++)
	  {
		  for (int j = 0; j<columns ;j++)
		  {
			  cout<<matrix[i][j];
			  cout<<"  ";
		  }
	   cout<<endl;
	  }
 }

};
int main()
{
	Matrix matrix(4,6);
	matrix.SetValues();
	Matrix matrix2(4,6);
	matrix.SetValues();

	Matrix c(4,6);
	c = matrix + matrix2;
	c.Print();
	cout<<endl;

	cout<<matrix.GetNumber(3,3); 
	cout<<endl;

	matrix.SetNumber(3,3, 5);
	matrix.Print();
	cout<<endl;

	matrix.ScalarMultiplication(5);
	matrix.Print();
	cout<<endl;


	matrix.DiagonalMatrix();
	matrix.Print();
	cout<<endl;
	
	matrix.IdentityMatrix();
	matrix.Print();
	cout<<endl;
	
	matrix.ZeroMatrix();
	matrix.Print();
	cout<<endl;
	
	system("Pause");
	return 0;
}

If the operator is implemented as a class method, it shall take one parameter instead of two (the first operand is *this). If you implement it outside the class, then you need to supply the first operand either.
And you should add the 'const' modifier to the parameters:

Code:

Matrix operator + (const Matrix& A) {
}

Whenever you say 'I'm getting error' please tell what the error message is.

Code:

 void operator = (Matrix a, Matrix b)
 {
	 //if a and b are equal 
	 //then assign b to a
	
	 for (int i = 0; i< rows; i++)
	 {
		  for (int j = 0; j< columns ;j++)
		  {
			  a[i][j] = b[i][j];
		  }
	 }
	
 }

What does the comment mean? Even if you implement this operator as a global function, it wouldn't work since you use a copy of 'Matrix'. The first operand should be Matrix& and the second one const Matrix&.

I meant declaring it as a global function, but stick to the class method idea, that is:

Code:

class Matrix {

// ...

Matrix& operator = (const Matrix& A)
{
    for (int i = 0; i< rows; i++)
    {
        for (int j = 0; j< columns ;j++)
        {
            matrix[i][j] = A.matrix[i][j];
	}
    }
    return *this;
}

};

AND:

1. supply the destructor to delete[] the matrix!
2. be careful with the rows and columns, as they might differ in size (like in the operator above).
3. supply the [] operator:

Code:

int* operator [] (int index) {
    return matrix[index];
}
const int* operator [] (int index) const {
    return matrix[index];
}

The + operator shall have the const modifier too.

I meant declaring it as a global function, but stick to the class method idea, that is:

The compiler would inform you that operator= cannot be overloaded as a global function.