/in/foo.cc: In function 'void make_tree(int, int)':
/in/foo.cc:13:16: warning: array subscript has type 'char' [-Wchar-subscripts]
   if (map[s1[i]]<k)
                ^
/in/foo.cc:15:15: warning: array subscript has type 'char' [-Wchar-subscripts]
    k=map[s1[i]];
               ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:26:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s1);
  ^~~~
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:26:9: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s1);
         ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:27:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s2);
  ^~~~
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:27:9: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s2);
         ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:30:12: warning: array subscript has type 'char' [-Wchar-subscripts]
   map[s2[i]]=i;
            ^
/in/foo.cc: In function 'void make_tree(int, int)':
/in/foo.cc:19:18: warning: 'where' may be used uninitialized in this function [-Wmaybe-uninitialized]
  putchar(s1[where]);
          ~~~~~~~~^
/tmp/cczUpLOD.o: In function `main':
foo.cc:(.text.startup+0xc): warning: the `gets' function is dangerous and should not be used.