duff's device: literal spaghetti code!

duff.c

/**
 * A demonstration of Duff's Device,
 * which entangles a switch/case statement
 * with another C idiom, like a do/while.
 *
 * https://en.wikipedia.org/wiki/Duff%27s_device
 */
#include <stdlib.h>
#include <stdio.h>

int main(int argc, char** argv) {

    if(argc < 2) {
        return 1;
    }
    const int input = strtol(argv[1], NULL, 10);
    printf("%d\n", input);

    int n = (input + 3) / 4;

    int output = 0;

    // The good stuff
    switch (input % 4) {
        case 0:  do { output++;
        case 3:       output++;
        case 2:       output++;
        case 1:       output++;
                 } while( n --> 0); // Another fun one: Equivalent to --n > 0
    }

    printf("%d\n", output);

    return 0;
}