Question

How to add and multiply two matrices in the following code?

#include "My_matrix.h"

#include <stdexcept>

My_matrix::My_matrix()

{

// add your code here

n = 0;

m = 0;

ptr = nullptr;

}

void My_matrix::allocate_memory()

{

// add your code here

ptr = new int* [n];

for (int i = 0; i < n; ++i) {

ptr[n] = new int[m];

}

}

My_matrix::My_matrix(int n1, int m1)

{

// add your code here

n = n1;

m = m1;

ptr = new int*[n];

for(int i = 0; i < n; i++) {

ptr[i] = new int[m];

}

for (int i = 0; i < n; i++) {

for (int j = 0; j < m; j++) {

ptr[i][j] = 0;

}

}

}

My_matrix::My_matrix(const My_matrix& mat)

{

// add your code here

this->n = mat.n;

this->m = mat.m;

ptr = new int*[n];

for(int i = 0; i < n; i++) {

ptr[i] = new int[m];

}

for (int i = 0; i < mat.n; i++) {

for (int j = 0; j < mat.m; j++) {

this->ptr[n][m] = mat.ptr[n][m];

}

}  

}

My_matrix::~My_matrix()

{

// add your code here

for (int i = 0; i < n; ++i) {

delete [] ptr[i];

}

delete [] ptr;

}

My_matrix& My_matrix::operator=(const My_matrix& mat)

{

// add your code here

   this->n = mat.n;

this->m = mat.m;

ptr = new int*[n];

for(int i = 0; i < n; i++) {

ptr[i] = new int[m];

}

for (int i = 0; i < mat.n; i++) {

for (int j = 0; j < mat.m; j++) {

this->ptr[n][m] = mat.ptr[n][m];

}

}

   }

int My_matrix::number_of_rows() const

{

// add your code here

return n;

}

int My_matrix::number_of_columns() const

{

// add your code here

return m;

}

int* My_matrix::operator()(int i) const

{

// add your code here

return ptr[i];

}

int My_matrix::operator()(int i, int j) const

{

// add your code here

   return ptr[n][m];

}

int& My_matrix::operator()(int i, int j)

{

// add your code here

return ptr[n][m];

}

int My_matrix::elem(int i, int j) const

{

if (i < 0 || i >= n) throw out_of_range("Out of range");

if (j < 0 || j >= m) throw out_of_range("Out of range");

// add your code here

return ptr[n][m];

}

int& My_matrix::elem(int i, int j)

{

// add your code here

if (i < 0 || i >= n) throw out_of_range("Out of range");

if (j < 0 || j >= m) throw out_of_range("Out of range");

return ptr[n][m];

}

ostream& operator<<(ostream& out, const My_matrix& mat)

{

// add your code here

for (int i = 0; i < mat.number_of_rows(); i++) {

for (int j = 0; j < mat.number_of_columns(); j++) {

out << mat(i, j) << " ";

}

out << endl;

}

return out;

}

istream& operator>>(istream& in, My_matrix& mat)

{

// add your code here

for(int i = 0; i < mat.number_of_rows(); i++ ){

for(int j = 0; j < mat.number_of_columns(); j++){

in >> mat(i, j);

}

}

return in;

}

My_matrix operator+(const My_matrix& mat1, const My_matrix& mat2)

{ // add your code here

}

My_matrix operator*(const My_matrix& mat1, const My_matrix& mat2)

{

// add your code here

}

Answer 1

// Add two matrices

// for adding 2 matrices we should have same number of columns and rows in both matrices

My_matrix operator+(const My_matrix& mat1, const My_matrix& mat2)

{ // add your code here

int r1 = mat1.number_of_rows();

int c1 = mat1.number_of_columns();

int r2 = mat2.number_of_rows();

int c2 = mat2.number_of_columns();

if (r1 !=r2 || c1!=c2){

out<<"can not add these matrices";

} else {

int sum[r1][c1], i, j;

  // Add matrices
  for(i = 0; i < r1; ++i)
    for(j = 0; j < c1; ++j)
      sum[i][j] = a[i][j] + b[i][j];
  // Displaying the resultant sum matrix.
  out << endl << "resultant matrix is: " << endl;
  for(i = 0; i < r1; ++i)
    for(j = 0; j < c1; ++j) {
      cout << sum[i][j] << "  ";
      if(j == c - 1)
        out << endl;
      }  
  }

}

/// lMultiply 2 matrices

// we can multiply 2 matrices only if column of 1st matrix is same as rows of second matrix. c1=r2;

My_matrix operator*(const My_matrix& mat1, const My_matrix& mat2)

{

// add your code here

if (c1 !=r2){

out<<"can not multiply these matrices";

} else {

int r1 = mat1.number_of_rows();

int c1 = mat1.number_of_columns();

int r2 = mat2.number_of_rows();

int c2 = mat2.number_of_columns();

int row = r1;

int col = c2;

mul[r1][c2];

///////

// Initializing mat mul 0.
    for(i = 0; i < r1; ++i)
        for(j = 0; j < c2; ++j)
        {
            mul[i][j]=0;
        }

    // store the multiplication result.
    for(i = 0; i < r1; ++i)
        for(j = 0; j < c2; ++j)
            for(k = 0; k < c1; ++k)
            {
                mul[i][j] += mat1[i][k] * mat2[k][j];
            }

    // Displaying the multiplication of two matrix.
    for(i = 0; i < r1; ++i)
    for(j = 0; j < c2; ++j)
    {
        out << " " << mul[i][j];
        if(j == c2-1)
            cout << endl;
    }

//////

}

}