Define class matrix of integers using vector - c++

Question

I have run the following code.
Errors I got are: invalid types array subscripts
Is there any mistake in using the constructor?
While I run it normally without using any constructor, I got an error output.
These are the errors I got, please check out what my mistake is:
invalid types 'const int[int]' for array subscript inside the = operator
and
[Error] invalid types 'int[int]' for array subscript inside print function in the program.
#include<iostream>
#include<vector>
using namespace std;
class Matrix
{
int i,j,x,y;
vector<int> v;
vector<int> b;
public:
Matrix()
{
}
Matrix(int m, int n) //Main constructor
{
x=m;
y=n;
vector< vector <int> > v(x,vector <int>(y));
cout<< "enter values into the vector" << endl;
for(int i = 0; i < x; ++i)
{
for (int j = 0; j < y; ++j)
{
cin >> v[i][j];
}
}
}
Matrix(const Matrix &t)
{
x=t.x;
y=t.y;
v=t.v;
cout << "copy constructor called" << endl;
}
~matrix()
{
cout << "destructor called" << endl;
}
Matrix operator=( const Matrix &r)
{
x=r.x;
y=r.y;
vector< vector <int> > b(x,vector <int>(y));
for (i=0;i<x;++i)
{
for (j=0;j<y;++j)
{
b[i][j]=r.v[i][j];
}
}
for (int i = 0; i < x; i++)
{
for (int j = 0; j < y; j++)
{
cout << b[i][j] << " ";
}
cout << endl;
}
}
void print()
{
for (i = 0; i < x; i++)
{
for (j = 0; j < y; j++)
{
cout << v[i][j] << " ";
}
cout << endl;
}
}
};
int main()
{
int d1,d2;
cout << "enter row,column values" << endl;
cin >> d1 >> d2;
Matrix ob1();
Matrix ob2(d1,d2);
cout << "elements in the matrix using constructor are" << endl;
ob2.print();
Matrix ob3(ob2);
cout << "elements in the copy constructor" << endl;
ob3.print();
cout << "after overloading assignment operator" << endl;
Matrix ob4;
ob4=ob2;
return 0;
}
Thank you in advance. It looks there is too much code with respect to text in this question, so needed to add a few words here.

Answer 1

As #Federico quickly spotted, class data v is initially defined just as a vector<int>, but then used throughout the member functions as vector< vector<int> >.
No need to define b and loop indices i,j as class data.
In addition, v in the assignment operator was redefined locally, so even after having correctly compiled, the program would not have yielded the desired results.
This MWE below should work as intended
#include<iostream>
#include<vector>
using namespace std;
class Matrix
{
int x,y; // redundant class data erased
vector< vector <int> > v;
public:
Matrix(): x(0), y(0), v(0)
{
}
Matrix(int m, int n) // Main constructor
{
x=m;
y=n;
v = vector< vector<int> >(x,vector <int>(y, 0)); // in original version, this class data was redefined locally
cout<< "enter values into the vector" << endl;
for(int i = 0; i < x; ++i)
{
for (int j = 0; j < y; ++j)
{
cin >> v[i][j];
}
}
}
Matrix(const Matrix &t)
{
x=t.x;
y=t.y;
v=t.v;
cout << "copy constructor called" << endl;
}
~Matrix()
{
cout << "destructor called" << endl;
}
Matrix& operator=(const Matrix &r) // needs to output a reference
{
if (this == &r) // check self-assignment
return *this;
x = r.x;
y = r.y;
vector< vector<int> > b(x,vector <int>(y, 0));
for (int i = 0; i < x; ++i)
{
for (int j = 0; j < y; ++j)
{
b[i][j] = r.v[i][j];
}
}
for (int i = 0; i < x; i++)
{
for (int j = 0; j < y; j++)
{
cout << b[i][j] << " ";
}
cout << endl;
}
return *this;
}
void print()
{
for (int i = 0; i < x; i++)
{
for (int j = 0; j < y; j++)
{
cout << v[i][j] << " ";
}
cout << endl;
}
}
};
int main()
{
int d1,d2;
cout << "enter row, column values" << endl;
cin >> d1 >> d2;
Matrix ob1();
Matrix ob2(d1,d2);
cout << "elements in the matrix using constructor are" << endl;
ob2.print();
Matrix ob3(ob2);
cout << "elements in the copy constructor" << endl;
ob3.print();
cout << "after overloading assignment operator" << endl;
Matrix ob4;
ob4=ob2;
return 0;
}
Output:
enter row, column values
3 3
enter values into the vector
1 2 3 4 5 6 7 8 9
elements in the matrix using constructor are
1 2 3
4 5 6
7 8 9
copy constructor called
elements in the copy constructor
1 2 3
4 5 6
7 8 9
after overloading assignment operator
1 2 3
4 5 6
7 8 9
destructor called
destructor called
destructor called