runner% cat ranwalk.c
/* Random walk in the plane.
 * Written by NR Wagner, 23 April 1997
 */
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define MAXP 75

void blank_plane(char plane[][MAXP]);
void one_step(int x, int y, int *new_x, int *new_y);
void print_plane(char plane[][MAXP], int steps);

void main(void)
{
        char plane[MAXP][MAXP];
        char alf[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
             "abcdefghijklmnopqrstuvwxyz";
        int steps = 0;
        int x = 40, y = 40; /* initial location */
        int new_x, new_y;
        srand48((long)time(NULL));
        blank_plane(plane);
        while( x >= 0 && x < MAXP && y >= 0 && y < MAXP) {
                steps++;
                plane[x][y] = alf[(steps/50)%52];
                one_step(x, y, &new_x, &new_y);
                x = new_x; y = new_y;
        }
        print_plane(plane, steps);
}

void blank_plane(char plane[][MAXP])
{
        int i, j;
        for(i = 0; i < MAXP; i++)
                for(j = 0; j < MAXP; j++)
                        plane[i][j] = ' ';
}

void one_step(int x, int y, int *new_x, int *new_y)
{
        if (drand48() < 0.5) { /* change x */
                *new_y = y;
                if (drand48() < 0.5) *new_x = x + 1.0;
                else *new_x = x - 1.0;
        }
        else { /* change y */
                *new_x = x;
                if (drand48() < 0.5) *new_y = y + 1.0;
                else *new_y = y - 1.0;
        }
}

void print_plane(char plane[][MAXP], int steps)
{
        int i, j;
        printf("Number of steps to the boundary: %i\n",
                steps);
        printf("   ");
        for(j = 0; j < MAXP; j++)
                printf("%i", j/10);
        printf("|\n");
        printf("   ");
        for(j = 0; j < MAXP; j++)
                printf("%i", j%10);
        printf("|\n");
        printf("   ");
        for(j = 0; j < MAXP; j++)
                printf("-");
        printf("|\n");
        for(i = 0; i < MAXP; i++) {
                printf("%2i|", i);
                for(j = 0; j < MAXP; j++)
                        printf("%c", plane[i][j]);
                printf("|\n");
        }
        printf("   ");
        for(j = 0; j < MAXP; j++)
                printf("-");
        printf("|\n");
}
runner% cc -o ranwalk ranwalk.c
runner% ranwalk
Number of steps to the boundary: 2756
   000000000011111111112222222222333333333344444444445555555555666666666677777|
   012345678901234567890123456789012345678901234567890123456789012345678901234|
   ---------------------------------------------------------------------------|
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10|                                                                           |
11|                                                                           |
12|                                                      KK                   |
13|                                                      KKKK                 |
14|                                                     KKKKL                 |
15|                                                        KLL     NN         |
16|                                                       KKLLL   NNN         |
17|                                                       KLLLL   NNN         |
18|                                                       K LL    N N         |
19|                                             G        KK LL   NN NN        |
20|                                             GGG     KKKJLLPPPPP  N        |
21|                                      EE     GGGG   KKKJJJOPPPQRRRRM       |
22|                                       EEEDDGGG G  KKKKJJJOPLLRRRRPUP      |
23|                                      DEEEEDGG  G   KJKKJJ feeRRRRUUTQQ    |
24|                                      DEDEEGGG FGG   JKKI OffeSeURUUTQQ    |
25|                                       DDEEEFFFFFGGGGIKKI ffSeeeUUUUUQ     |
26|                                      DDDEEEF  F   GIIIIIfffSeeeUUUU       |
27|                                         DFFFFFF    IIIIffHfSeeeUUU        |
28|                                        CCCFEFF        IffHffeefeeXXX X    |
29|                                        CCCFFFF        HHfffffffedXXXXX    |
30|                                         CCCFFF           fffffWddWXX X    |
31|                                         CCCCCC            ff  Wdd VVVXV   |
32|                                         CCC              fffWWWWdVVVVXV   |
33|                                        BBCC             gg WWWdddd  VXV   |
34|                                      BBBB               g  ddWWWddd  X    |
35|                                        BB               gggggddddd   X    |
36|                                        AA                 ggg    d  XX    |
37|                                       AAA               gggggd   X  XXX   |
38|                                       AAAA              cgggcdd  Y   XX   |
39|                                      AAAAA               ccggg   YYXXXX   |
40|                                      A AAA                  gg  YYYY      |
41|                                         AA                ggg Z YYY       |
42|                                                           ggccZZYYY       |
43|                                                            gccZZZZY       |
44|                                                            gccjZaaa       |
45|                                                            gkkkjaaaa      |
46|                                                           bgkkkjaj        |
47|                                          rqq              ggbbkkaj        |
48|                                         qrrqpp      h  hhbgbhhkkkkj       |
49|                                         qrrqpp      hhhhhhnhhbkjhjj       |
50|                                         qrrrqpwwwo  o hhnnnnaakjljj       |
51|                                         qrttuuwowoooo nnnnnninnlllj       |
52|                                       sqqttuuwwww   oooo  mnnnnlllj       |
53|                                       sssttvuwvov     oo  mmnnnllljj      |
54|                                       ssqtvvvwwwww       nnnn lllljj      |
55|                                       ss tvuuwwwww       nmm llll         |
56|                                    sss s uvuwwwwxw       mmmmml           |
58|                                    s svvvvvv rxxxyy        mmll           |
59|                                    sssvvv yy  xxyyy                       |
60|                                          yyyyyyxxyzz                      |
61|                                          yyyyyyBBz                        |
62|                                                ABBB                       |
63|                                                ABBBB                      |
64|                                                ABBBBB                     |
65|                                               AABBBBB                     |
66|                                               AACCCBz                     |
67|                                         CCCCCCCCCCCzzzz                   |
68|                                           CCC   AC  Azz                   |
69|                                         CCC      AA AAz                   |
70|                                          CCC      AAAz                    |
71|                                           CCCCC   AAA                     |
72|                                            CCCC                           |
73|                                           DD                              |
74|                                           D                               |
   ---------------------------------------------------------------------------|