hanoi.c

#include <stdio.h> 
#include <stdlib.h>

static void
hanoi(unsigned char n)
{
	void *s[32];
	char p[3] = "ABC", t;

	if (n >= 32) n = 31;
	s[n] = &&step_3;
step_0:
	if (n == 0) goto *s[n++];
	// ABC => ACB
	t = p[1], p[1] = p[2], p[2] = t;
	s[--n] = &&step_1;
	goto step_0;
step_1:
	// A -> C
	printf("%c -> %c\n", p[0], p[1]);
	// ACB => BAC
	t = p[0], p[0] = p[2], p[2] = p[1], p[1] = t;
	s[--n] = &&step_2;
	goto step_0;
step_2:
	// BAC => ABC
	t = p[1], p[1] = p[0], p[0] = t;
	goto *s[n++];
step_3:
	return;
}

int main(int argc, char *argv[])
{
	if (argc != 2)
		fprintf(stderr,
			"usage: %s [n]\n\tPrint hanoi sequence of n discs.\n",
			argv[0]);
	else
		hanoi(atoi(argv[1]));
	return 0;
}