How can i multiply matrices by overloading * operator, when the operator doesn't matches the operands?

I have two matrices which should multiply together by overloading * operator in the constructor class, but the problem here is that no operator [] matches these operands. Why?

I saw videos and asked my classmates multiple times and tried my own way, but I can't make it work!! I only get this error!!

This is the code I have a problem with:

The Constructor Code:

I made two ways to make this code works. The result should store at cell matrix or the new matrix:

Matrix operator*(const Matrix &matrix1, const Matrix &matrix2)
  {
    if (matrix1.Cols != matrix2.Rows) {
        throw("Error");
    }
    cell.resize(matrix2.Cols); // one way to call 
    Matrix res(matrix1.Rows, matrix2.Cols, 1.0); // second way to call
    for (int i = 0; i < matrix1.Rows; i++) {
        cell[i].resize(matrix1.Rows);
        for (int j = 0; j < matrix2.Cols; j++) {
            double value_of_elements;
            for (int k = 0; k = matrix1.Cols; k++) {
                res[i][j] += matrix1[i][k] * matrix2[i][j];// 
   1. metod
                value_of_elements += matrix1[i][k] * 
    matrix2[i][j];// 2. metod
            }
            cell[i][j]+=value_of_elements;
        }
    }
    return res;
   }

The Header Code:

The header code normally I don't have unless some modification should be made.

friend Matrix operator*(const Matrix &matrix1, const Matrix &matrix2);

The source Code:

This is where the code is tested:

try {

        Matrix m1(3, 3, 1.0);
        Matrix m2(3, 4, 1.0);

        std::cout << "m1*m2:" << m1 * m2 << std::endl;// this si where the matrix should be multiplied here;

    }
    catch (std::exception &e) {
        std::cout << "Exception: " << e.what() << "!" << std::endl;
    }
    catch (...) {
        std::cout << "Unknown exception caught!" << std::endl;
    }
   system("pause");
   return 0;
}

The result:

The result should be this:

m1*m2:[3, 3, 3, 3
3, 3, 3, 3
3, 3, 3, 3]

What I get is an error; the cause of error are that res[i][j], matrix1[i][k] etc. have operators [] wont work on these operands.