Language: C

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#include<stdio.h>
 
int main(){
 
char buf[20];
int i;
scanf("%s",&buf);
 
for(i=20;i>0;i--){
 
if(buf[i]=='\0'){
break;
}
 
}
 
for(i=i;i>0;i--){
printf("%c",buf[i]);
}
printf("%n");
 
return 0;
}
 

Compiler output:
main.c:1:1: error: expected identifier or '(' before numeric constant
    1 | 4
      | ^
In file included from /usr/include/stdio.h:47,
                 from main.c:22:
/usr/include/x86_64-linux-gnu/bits/types/cookie_io_functions_t.h:28:43: error: unknown type name 'size_t'
   28 |                                           size_t __nbytes);
      |                                           ^~~~~~
/usr/include/x86_64-linux-gnu/bits/types/cookie_io_functions_t.h:1:1: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
  +++ |+#include <stddef.h>
    1 | /* Copyright (C) 1991-2025 Free Software Foundation, Inc.
/usr/include/x86_64-linux-gnu/bits/types/cookie_io_functions_t.h:37:44: error: unknown type name 'size_t'
   37 |                                            size_t __nbytes);
      |                                            ^~~~~~
/usr/include/x86_64-linux-gnu/bits/types/cookie_io_functions_t.h:37:44: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/x86_64-linux-gnu/bits/types/cookie_io_functions_t.h:57:3: error: unknown type name 'cookie_read_function_t'; did you mean 'cookie_seek_function_t'?
   57 |   cookie_read_function_t *read;         /* Read bytes.  */
      |   ^~~~~~~~~~~~~~~~~~~~~~
      |   cookie_seek_function_t
/usr/include/x86_64-linux-gnu/bits/types/cookie_io_functions_t.h:58:3: error: unknown type name 'cookie_write_function_t'; did you mean 'cookie_close_function_t'?
   58 |   cookie_write_function_t *write;       /* Write bytes.  */
      |   ^~~~~~~~~~~~~~~~~~~~~~~
      |   cookie_close_function_t
/usr/include/stdio.h:314:35: error: unknown type name 'size_t'
  314 | extern FILE *fmemopen (void *__s, size_t __len, const char *__modes)
      |                                   ^~~~~~
/usr/include/stdio.h:130:1: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
  129 | #include <bits/stdio_lim.h>
  +++ |+#include <stddef.h>
  130 | 
/usr/include/stdio.h:320:47: error: unknown type name 'size_t'
  320 | extern FILE *open_memstream (char **__bufloc, size_t *__sizeloc) __THROW
      |                                               ^~~~~~
/usr/include/stdio.h:320:47: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:340:34: error: unknown type name 'size_t'
  340 |                     int __modes, size_t __n) __THROW __nonnull ((1));
      |                                  ^~~~~~
/usr/include/stdio.h:340:34: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:346:24: error: unknown type name 'size_t'
  346 |                        size_t __size) __THROW __nonnull ((1));
      |                        ^~~~~~
/usr/include/stdio.h:346:24: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:385:44: error: unknown type name 'size_t'
  385 | extern int snprintf (char *__restrict __s, size_t __maxlen,
      |                                            ^~~~~~
/usr/include/stdio.h:385:44: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:389:45: error: unknown type name 'size_t'
  389 | extern int vsnprintf (char *__restrict __s, size_t __maxlen,
      |                                             ^~~~~~
/usr/include/stdio.h:389:45: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:690:30: error: unknown type name 'size_t'
  690 |                              size_t *__restrict __n, int __delimiter,
      |                              ^~~~~~
/usr/include/stdio.h:690:30: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:693:28: error: unknown type name 'size_t'
  693 |                            size_t *__restrict __n, int __delimiter,
      |                            ^~~~~~
/usr/include/stdio.h:693:28: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:698:27: error: unknown type name 'size_t'
  698 |                           size_t *__restrict __n,
      |                           ^~~~~~
/usr/include/stdio.h:698:27: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:728:8: error: unknown type name 'size_t'
  728 | extern size_t fread (void *__restrict __ptr, size_t __size,
      |        ^~~~~~
/usr/include/stdio.h:728:8: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:728:46: error: unknown type name 'size_t'
  728 | extern size_t fread (void *__restrict __ptr, size_t __size,
      |                                              ^~~~~~
/usr/include/stdio.h:728:46: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:729:22: error: unknown type name 'size_t'
  729 |                      size_t __n, FILE *__restrict __stream) __wur
      |                      ^~~~~~
/usr/include/stdio.h:729:22: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:735:8: error: unknown type name 'size_t'
  735 | extern size_t fwrite (const void *__restrict __ptr, size_t __size,
      |        ^~~~~~
/usr/include/stdio.h:735:8: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:735:53: error: unknown type name 'size_t'
  735 | extern size_t fwrite (const void *__restrict __ptr, size_t __size,
      |                                                     ^~~~~~
/usr/include/stdio.h:735:53: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:736:23: error: unknown type name 'size_t'
  736 |                       size_t __n, FILE *__restrict __s) __nonnull((4));
      |                       ^~~~~~
/usr/include/stdio.h:736:23: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:756:8: error: unknown type name 'size_t'
  756 | extern size_t fread_unlocked (void *__restrict __ptr, size_t __size,
      |        ^~~~~~
/usr/include/stdio.h:756:8: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:756:55: error: unknown type name 'size_t'
  756 | extern size_t fread_unlocked (void *__restrict __ptr, size_t __size,
      |                                                       ^~~~~~
/usr/include/stdio.h:756:55: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:757:31: error: unknown type name 'size_t'
  757 |                               size_t __n, FILE *__restrict __stream) __wur
      |                               ^~~~~~
/usr/include/stdio.h:757:31: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:759:8: error: unknown type name 'size_t'
  759 | extern size_t fwrite_unlocked (const void *__restrict __ptr, size_t __size,
      |        ^~~~~~
/usr/include/stdio.h:759:8: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:759:62: error: unknown type name 'size_t'
  759 | extern size_t fwrite_unlocked (const void *__restrict __ptr, size_t __size,
      |                                                              ^~~~~~
/usr/include/stdio.h:759:62: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'
/usr/include/stdio.h:760:32: error: unknown type name 'size_t'
  760 |                                size_t __n, FILE *__restrict __stream)
      |                                ^~~~~~
/usr/include/stdio.h:760:32: note: 'size_t' is defined in header '<stddef.h>'; this is probably fixable by adding '#include <stddef.h>'