Notice that your own post illustrates why this is a bad idea; whereas
for(int i=0;i<N;i++){
}
correctly steps through `N` `i`-values, a version with your `all_frob_indices` would step through `N + 1` `i`-values (because your termination check is `i > N`). Of course, it's easy to fix this once it's spotted, but you won't spot it with the same ease that you'd spot an off-by-one error in a `for` loop, because your eyes (or at least my eyes) don't know how an `all_frob_indices` function should look as well as they do how a `for` loop should look.
