foo.cc: In function 'int main()':
foo.cc:16:31: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
   16 |         for (i=0;i<L;i++) gets(I[i]);
      |                           ~~~~^~~~~~
In file included from /nix/store/42izybv2fz3ps5pcg3dvcmn85pc9406y-gcc-11.3.0/include/c++/11.3.0/cstdio:42,
                 from stdc++.h:46:
/nix/store/ck17nf5q2m51d9jpkpsirx91s64vh202-glibc-2.35-163-dev/include/stdio.h:605:14: note: declared here
  605 | extern char *gets (char *__s) __wur __attribute_deprecated__;
      |              ^~~~
foo.cc:20:26: warning: array subscript has type 'char' [-Wchar-subscripts]
   20 |                 if (f[n[0]]++) break; //err: used variable
      |                       ~~~^
foo.cc:20:27: warning: use of an operand of type 'bool' in 'operator++' is deprecated [-Wdeprecated]
   20 |                 if (f[n[0]]++) break; //err: used variable
      |                     ~~~~~~^
foo.cc:31:27: warning: array subscript has type 'char' [-Wchar-subscripts]
   31 |                 f[S.top().first]=0;
      |                   ~~~~~~~~^~~~~
foo.cc:37:38: warning: array subscript has type 'char' [-Wchar-subscripts]
   37 |         while (!S.empty()) f[S.top().first]=0, S.pop();
      |                              ~~~~~~~~^~~~~
/nix/store/dpxy5cr7cm0nch0qvq2qygs9jwnmhiy5-binutils-2.38/bin/ld: /tmp/ccemOvKV.o: in function `main':
foo.cc:(.text.startup+0x8f): warning: the `gets' function is dangerous and should not be used.

[Hydro](https://hydro.ac)提供评测服务