Sample solution

#include <cstddef> /* needed for std::size_t  and std::ptrdiff_t */
#include <printf.hpp> /* needed for fmt::printf */

struct Matrix {
   std::size_t m; /* number of rows */
   std::size_t n; /* number of columns */
   std::ptrdiff_t incRow;
   std::ptrdiff_t incCol;
   double* data;

   void init() {
      for (std::size_t i = 0; i < m; ++i) {
         for (std::size_t j = 0; j < n; ++j) {
            data[i*incRow + j*incCol] = j * m + i + 1;
         }
      }
   }

   void print() {
      for (std::size_t i = 0; i < m; ++i) {
         fmt::printf("  ");
         for (std::size_t j = 0; j < n; ++j) {
            fmt::printf(" %4.1lf", data[i*incRow + j*incCol]);
         }
         fmt::printf("\n");
      }
   }
};

int main() {
   Matrix A;
   A.m = 7; A.n = 8;
   A.data = new double[A.m * A.n];
   A.incRow = 1; A.incCol = 7;
   A.init();
   fmt::printf("A =\n"); A.print();
   delete[] A.data;
}
theon$ g++ -std=gnu++11 -o matrix_class2 matrix_class2.cpp
theon$ ./matrix_class2
A =
    1.0  8.0 15.0 22.0 29.0 36.0 43.0 50.0
    2.0  9.0 16.0 23.0 30.0 37.0 44.0 51.0
    3.0 10.0 17.0 24.0 31.0 38.0 45.0 52.0
    4.0 11.0 18.0 25.0 32.0 39.0 46.0 53.0
    5.0 12.0 19.0 26.0 33.0 40.0 47.0 54.0
    6.0 13.0 20.0 27.0 34.0 41.0 48.0 55.0
    7.0 14.0 21.0 28.0 35.0 42.0 49.0 56.0
theon$