Language: C

h#include <stdio.h>
#include <stdbool.h>
#include <string.h>

bool wall[10000][10000][4];
char str[10001];

const int U = 0;
const int R = 1;
const int D = 2;
const int L = 3;

char dirchar[] = "URDL" ;
int righthand(int x) {return (x+1)%4;}
int lefthand(int x) {return (x+3)%4;}
int dx[] = {0, 1, 0, -1};
int dy[] = {-1, 0, 1, 0};

int main() {
  bool firsttime = true;
  int width, height=0, i;
  int dir = R, x = 1, y = 0;

  while (true) {
    height++;
    scanf("%9999s\n", str);

    if (firsttime) {
      width = strlen(str)+2;
      firsttime = false;
    }

    for (i = 0; i<width-2; i++) {
      wall[i+1][height][U] = wall[i+1][height-1][D] = (str[i] == '1');
    }

    if (scanf("%10000s\n", str) == -1) {
      break;
    }

    for (i=0; i<width-1; i++) {
      wall[i][height][R] = wall[i+1][height][L] = (str[i] == '1');
    }
  }
  height++;

  firsttime = true;
  while (true) {
    if (!firsttime && 
	((x == 1 && y == 0) ||
	 (x == 0 && y == 1) ||
	 (x == 1 && y == 1)) &&
	wall[x][y][righthand(dir)]) {
      putchar(dirchar[dir]);
      break;
    }

    if (!wall[x][y][righthand(dir)]) {
      dir = righthand(dir);
      x += dx[dir];
      y += dy[dir];
    } else if (wall[x][y][dir]) {
      putchar(dirchar[dir]);
      dir = lefthand(dir);
    } else {
      x += dx[dir];
      y += dy[dir];
      putchar(dirchar[dir]);
    }

    firsttime = false;
  }

  puts("");

  return 0;
}

Compiler output:
main.c:1:2: error: stray '#' in program
    1 | h#include <stdio.h>
      |  ^
main.c:1:1: error: unknown type name 'h'
    1 | h#include <stdio.h>
      | ^
main.c:1:11: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token
    1 | h#include <stdio.h>
      |           ^
In file included from main.c:3:
/usr/include/string.h:44:22: error: unknown type name 'size_t'
   44 |                      size_t __n) __THROW __nonnull ((1, 2));
      |                      ^~~~~~
/usr/include/string.h:34:1: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
   33 | #include <stddef.h>
  +++ |+#include <stddef.h>
   34 | 
/usr/include/string.h:47:56: error: unknown type name 'size_t'
   47 | extern void *memmove (void *__dest, const void *__src, size_t __n)
      |                                                        ^~~~~~
/usr/include/string.h:47:56: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:55:32: error: unknown type name 'size_t'
   55 |                       int __c, size_t __n)
      |                                ^~~~~~
/usr/include/string.h:55:32: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:61:42: error: unknown type name 'size_t'
   61 | extern void *memset (void *__s, int __c, size_t __n) __THROW __nonnull ((1));
      |                                          ^~~~~~
/usr/include/string.h:61:42: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:64:56: error: unknown type name 'size_t'
   64 | extern int memcmp (const void *__s1, const void *__s2, size_t __n)
      |                                                        ^~~~~~
/usr/include/string.h:64:56: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:80:60: error: unknown type name 'size_t'
   80 | extern int __memcmpeq (const void *__s1, const void *__s2, size_t __n)
      |                                                            ^~~~~~
/usr/include/string.h:80:60: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:107:48: error: unknown type name 'size_t'
  107 | extern void *memchr (const void *__s, int __c, size_t __n)
      |                                                ^~~~~~
/usr/include/string.h:107:48: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:145:53: error: unknown type name 'size_t'
  145 |                       const char *__restrict __src, size_t __n)
      |                                                     ^~~~~~
/usr/include/string.h:145:53: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:153:23: error: unknown type name 'size_t'
  153 |                       size_t __n) __THROW __nonnull ((1, 2));
      |                       ^~~~~~
/usr/include/string.h:153:23: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:159:57: error: unknown type name 'size_t'
  159 | extern int strncmp (const char *__s1, const char *__s2, size_t __n)
      |                                                         ^~~~~~
/usr/include/string.h:159:57: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:166:8: error: unknown type name 'size_t'
  166 | extern size_t strxfrm (char *__restrict __dest,
      |        ^~~~~~
/usr/include/string.h:166:8: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:167:54: error: unknown type name 'size_t'
  167 |                        const char *__restrict __src, size_t __n)
      |                                                      ^~~~~~
/usr/include/string.h:167:54: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:179:8: error: unknown type name 'size_t'
  179 | extern size_t strxfrm_l (char *__dest, const char *__src, size_t __n,
      |        ^~~~~~
/usr/include/string.h:179:8: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:179:59: error: unknown type name 'size_t'
  179 | extern size_t strxfrm_l (char *__dest, const char *__src, size_t __n,
      |                                                           ^~~~~~
/usr/include/string.h:179:59: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:195:45: error: unknown type name 'size_t'
  195 | extern char *strndup (const char *__string, size_t __n)
      |                                             ^~~~~~
/usr/include/string.h:195:45: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:293:8: error: unknown type name 'size_t'
  293 | extern size_t strcspn (const char *__s, const char *__reject)
      |        ^~~~~~
/usr/include/string.h:293:8: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:297:8: error: unknown type name 'size_t'
  297 | extern size_t strspn (const char *__s, const char *__accept)
      |        ^~~~~~
/usr/include/string.h:297:8: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:389:46: error: unknown type name 'size_t'
  389 | extern void *memmem (const void *__haystack, size_t __haystacklen,
      |                                              ^~~~~~
/usr/include/string.h:389:46: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:390:44: error: unknown type name 'size_t'
  390 |                      const void *__needle, size_t __needlelen)
      |                                            ^~~~~~
/usr/include/string.h:390:44: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:398:55: error: unknown type name 'size_t'
  398 |                         const void *__restrict __src, size_t __n)
      |                                                       ^~~~~~
/usr/include/string.h:398:55: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:401:53: error: unknown type name 'size_t'
  401 |                       const void *__restrict __src, size_t __n)
      |                                                     ^~~~~~
/usr/include/string.h:401:53: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:407:8: error: unknown type name 'size_t'
  407 | extern size_t strlen (const char *__s)
      |        ^~~~~~
/usr/include/string.h:407:8: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:413:8: error: unknown type name 'size_t'
  413 | extern size_t strnlen (const char *__string, size_t __maxlen)
      |        ^~~~~~
/usr/include/string.h:413:8: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/string.h:413:46: error: unknown type name 'size_t'
  413 | extern size_t strnlen (const char *__string, size_t __maxlen)
      |                                              ^~~~~~
/usr/include/string.h:413:46: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
In file included from /usr/include/features.h:523,
                 from /usr/include/x86_64-linux-gnu/bits/libc-header-start.h:33,
                 from /usr/include/string.h:26:
/usr/include/string.h:432:12: error: unknown type name 'size_t'
  432 | extern int __REDIRECT_NTH (strerror_r,
      |            ^~~~~~~~~~~~~~
/usr/include/string.h:432:12: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
In file included from /usr/include/string.h:462:
/usr/include/strings.h:34:54: error: unknown type name 'size_t'
   34 | extern int bcmp (const void *__s1, const void *__s2, size_t __n)
      |                                                      ^~~~~~
/usr/include/strings.h:24:1: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
   23 | #include <stddef.h>
  +++ |+#include <stddef.h>
   24 | 
/usr/include/strings.h:38:53: error: unknown type name 'size_t'
   38 | extern void bcopy (const void *__src, void *__dest, size_t __n)
      |                                                     ^~~~~~
/usr/include/strings.h:38:53: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/strings.h:42:31: error: unknown type name 'size_t'
   42 | extern void bzero (void *__s, size_t __n) __THROW __nonnull ((1));
      |                               ^~~~~~
/usr/include/strings.h:42:31: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/strings.h:120:61: error: unknown type name 'size_t'
  120 | extern int strncasecmp (const char *__s1, const char *__s2, size_t __n)
      |                                                             ^~~~~~
/usr/include/strings.h:120:61: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/strings.h:134:27: error: unknown type name 'size_t'
  134 |                           size_t __n, locale_t __loc)
      |                           ^~~~~~
/usr/include/strings.h:134: