/* draw a Hilbert Curve in ASCII */
#include <stdio.h>
#include <string.h>
#define ORDER 4                     /* order of the curve */
#define SIZE ((2<<ORDER)-1)
char m[SIZE][SIZE + 1];             /* the "screen" */
int x, y;                           /* current coordinates */
unsigned p;                         /* previous direction */
void s(unsigned d) {                /* draw a single step */
    int *a[2] = { &x, &y };         /* let us access x,y as array */
    m[y][x] = d == p ? "-|"[d & 1] : '+';   /* if same dir then draw line */
    *a[d & 1] += 1 - (d & 2);       /* move in one of 4 directions */
    m[y][x] = "-|"[d & 1];          /* draw a line depending on direction */
    *a[d & 1] += 1 - (d & 2);       /* move in one of 4 directions */
    p = d;                          /* save old direction */
} 
void h(int o, int r, unsigned d) {  /* recursive hilbert algorithm */
    if(o--) {                       /* keep lowering order until 0 */
        d += r;
        h(o, -r, d);
        s(d);
        d -= r;
        h(o, r, d);
        s(d);
        h(o, r, d);
        d -= r;
        s(d);
        h(o, -r, d);
    }
}
int main() {
    memset(m, ' ', sizeof m);       /* fill with space */
    h(ORDER, 1, 0);                 /* main algorithm */
    m[y][x] = '+';                  /* fill in the last point */
    for(y = 0; y < SIZE; y++)       /* null terminate each line */
    m[y][SIZE] = 0;
    for(y = 0; y < SIZE; y++)       /* output the entire thing */
    puts(m[y]);
    return 0;
}