[Animats]

You can write that in C, but it doesn't really do anything. It's equivalent to

    void f(int n, int a[]) {
    }

Why? So that you can write

    void f(int n, int m, int a[n][m]) {
    }

which declares a 2-dimensional array parameter. In that case, the "m" is used to compute the position in the array for a 2D array. The "m" doesn't do anything. This is equivalent to writing

   void f(int n, int m, int a[][m]) {
   }

This is C's minimal multidimensional array support, known by few and used by fewer.

Over a decade ago, I proposed that sizes in parameters should be checkable and readable I worked out how to make it work.[1] But I didn't have time for the politics of C standards.

[1] http://animats.com/papers/languages/safearraysforc43.pdf