Maybe I'm missing something, but that just looks like a regular C switch to me. Yeah, it has fall-through, but all C switches has fall-through unless you explic

Maybe I'm missing something, but that just looks like a regular C switch to me. Yeah, it has fall-through, but all C switches has fall-through unless you explicitly break. The point of Duff's device is that it interleaves two different structures: a switch and a loop. It's unusual because in structured languages you expect the lexical structure to be entirely hierarchical (you wouldn't have an if block that somehow overlapped with a for-loop, for instance). Duff's device breaks that assumption because it uses one control structure (the switch) to jump into the middle of a second control structure (the loop), and lexically, the switch is both inside the loop and outside of it. This is why lots of people when they first see it don't think it is even syntactically valid. A regular switch with fall-through doesn't violate the "hierarchical lexical structure" assumption in that way.