Comment by runald

https://www.chiark.greenend.org.uk/~sgtatham/coroutines.html

  int function(void) {
      static int i, state = 0;
      switch (state) {
          case 0: /* start of function */
          for (i = 0; i < 10; i++) {
              state = 1; /* so we will come back to "case 1" */
              return i;
              case 1:; /* resume control straight after the return */
          }
      }
  }

Huh, I didn't know you could put case statements arbitrarily anywhere inside a switch block in C. Past the initial WTF, it's a nice hack for implementing coroutines.