[mnaydin]

I am not able to understand how

  int (*ap3)[900000] = malloc(sizeof *ap3);

is nicer than

  int *a = malloc(900000 * sizeof *a);

Notice that, in the former case, the array elements must be accessed as (*ap3)[i] whereas in the latter case the usual method a[i] is fine.

[syockit]

Me neither. In the VLA use cases page he does that with multidimensional array too.

    int (*arr)[n][m] = malloc(sizeof *arr);

which you have to access with

    (*arr)[i][j]

I prefer doing

    int (*arr)[m] = malloc(n*sizeof(*arr));

though this separates m and n to be one on left side while the other on the right side, it allows me to index directly

    arr[i][j]

[teo_zero]

You don't use this technique to define a new array, but to get a pointer to an array you already have.

The goal is to have a pointer to the array, and not a pointer to the first element of the array.

Whether this is "nicer" or not, and whether this is what you need in your application, are out of the scope of the fine article.