Variable modified types are cool - you can use them to cast a raw pointer to a N times N matrix and the math works out - you can just do m[i][j] instead of m[i*N+j].

But the evil part is when you declare variable length arrays on the stack. There are exactly two possible scenarios - either you have an upper bound on the allocated size or you don't.

If you have an upper bound and it is reasonably small, use a fixed length array on the stack - there is no point in saving a few bytes on the stack.

If you don't have an upper bound, VLAs will blow your stack, given the right inputs.

If you need a way to allocate unbounded arrays in a LIFO pattern, which 99% of the time are tiny, use a dedicated index-incrementing allocator, falling back on malloc when necessary. You can even cast the resulting pointer to a variably modified type, so that sizeof math works out