often said that c++ is superset of c but below not following that [duplicate]

Question

#include <stdio.h>
 
void print(int m, int n, int arr[][n])
{
    int i, j;
    for (i = 0; i < m; i++)
      for (j = 0; j < n; j++)
        printf("%d ", arr[i][j]);
}
 
int main()
{
    int arr[][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
    int m = 3, n = 3;
    print(m, n, arr);
    return 0;
}

why this code is working in c but not in c++. seems like 2d array as a parameter with this does not work in c++.

Answer 1

Linked questions explain all the differences, but answering just for the code in the question,

why this code is working in c but not in c++

Code uses variable length array, VLA for short. C++ simply does not have that, so the code is invalid as C++.

Note that some compilers have extensions which may enable some non-standard features, such as VLA support in GNU C++. But it's generally a bad idea to use those, as there are several popular C++ compilers, and using non-standard extensions stops the code from compiling with other C++ compilers which don't have the same extension (or same syntax for the extension).