overloading the addition and multiplication operators for the matrix class - c++

Question

I implement the overloading of the addition and multiplication operators for the matrix class. I can't understand where the error is, or rather, I guess that there is an error in the declaration of operators, but I have no idea how to fix it specifically.
Can someone suggest a good book on object oriented programming. I feel that I am clearly lacking information
#include <iostream>
using namespace std;
template <typename T>
class MATRIX
{
private:
T** M;
int m;
int n;
public:
MATRIX()
{
n = m = 0;
M = nullptr;
}
MATRIX(int _m, int _n)
{
m = _m;
n = _n;
M = (T**) new T * [m];
for (int i = 0; i < m; i++)
M[i] = (T*)new T[n];
for (int i = 0; i < m; i++)
for (int j = 0; j < n; j++)
M[i][j] = 0;
}
MATRIX(const MATRIX& _M)
{
m = _M.m;
n = _M.n;
M = (T**) new T * [m];
for (int i = 0; i < m; i++)
M[i] = (T*) new T[n];
for (int i = 0; i < m; i++)
for (int j = 0; j < n; j++)
M[i][j] = _M.M[i][j];
}
T GetMij(int i, int j)
{
if ((m > 0) && (n > 0))
return M[i][j];
else
return 0;
}
void SetMij(int i, int j, T value)
{
if ((i < 0) || (i >= m))
return;
if ((j < 0) || (j >= n))
return;
M[i][j] = value;
}
void Print(const char* ObjName)
{
cout << "Object: " << ObjName << endl;
for (int i = 0; i < m; i++)
{
for (int j = 0; j < n; j++)
cout << M[i][j] << "\t";
cout << endl;
}
cout << "---------------------" << endl << endl;
}
MATRIX operator=(const MATRIX& _M)
{
if (n > 0)
{
for (int i = 0; i < m; i++)
delete[] M[i];
}
if (m > 0)
{
delete[] M;
}
m = _M.m;
n = _M.n;
M = (T**) new T * [m];
for (int i = 0; i < m; i++)
M[i] = (T*) new T[n];
for (int i = 0; i < m; i++)
for (int j = 0; j < n; j++)
M[i][j] = _M.M[i][j];
return *this;
}
MATRIX operator+(const MATRIX& _M) {
MATRIX M6(_M.n, _M.m);
for (int i = 0; i < n; i++)
{
for (int j = 0; j < m; j++)
M6.M[i][j] = _M.M[i][j]+this-> M[i][j];
}
return M6;
}
MATRIX operator*(const MATRIX& _M) {
MATRIX M5(_M.n, _M.m);
for (int i = 0; i < _M.n; i++)
{
for (int j = 0; j < _M.m; j++)
{
for (int k = 0; k < m; k++)
{
M5.M[i][j] += M[i][k]*_M.M[k][j];
}
}
}
return M5;
}
bool operator ==(const MATRIX& _M) {
return this->n == _M.n && this->m == _M.m;
}
bool operator !=(const MATRIX& _M) {
return !(this->n == _M.n && this->m == _M.m);
}
~MATRIX()
{
if (n > 0)
{
for (int i = 0; i < m; i++)
delete[] M[i];
}
if (m > 0)
delete[] M;
}
};
void main()
{
MATRIX<int> M(2, 3);
M.Print("M");
int i, j;
for (i = 0; i < 2; i++)
for (j = 0; j < 3; j++)
M.SetMij(i, j, i + j);
M.Print("M");
MATRIX<int> M2 = M;
M2.Print("M2");
MATRIX<int> M3;
M3 = M;
M3.Print("M3");
MATRIX<int> M4;
M4 = M3 = M2 = M;
M4.Print("M4");
////////////////////////
bool result = M == M3;// ==
if (result == 1) {
cout << "true";
}
else if (result == 0) {
cout << "false";
}
cout << endl << "---------------------" << endl << endl;
//////////////////////////
bool result1 = M != M3;// !=
if (result1 == 1) {
cout << "true";
}
else if (result1 == 0) {
cout << "false";
}
cout << endl << "---------------------" << endl << endl;
MATRIX<int> M1;
for (i = 0; i < 2; i++)
for (j = 0; j < 3; j++)
M1.SetMij(i, j, i + j);
M1.Print("M1");
M.Print("M");
MATRIX<int> M6 = M + M1;
M6.Print("M");
MATRIX<int> M5 = M * M1;
M5.Print("M");
}```
thanks in advance
[enter image description here][1]
[1]: https://i.stack.imgur.com/TjEOp.png

Answer 1

I belive that std::vector is better
MATRIX() {}
MATRIX(int r, int c) : M(r * c, T()) , rows(r), cols(c) { }
// Does not need copy constructor
// Does not need operator =
// Does not need destructor
also you can proxy row and cols to overload []
MATRIX<int> x(3,3);
x[2][2] = 10;
also a generating function is welcome
template<typename GenT> void generate( GenT gen ) {...}
https://godbolt.org/z/dK6Tqc