foo.c: In function 'main':
foo.c:18:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(s);
  ^~~~
In file included from foo.c:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
foo.c:21:7: warning: array subscript has type 'char' [-Wchar-subscripts]
   flag[s[i]]++;
       ^
/tmp/cc8Nt8mI.o: In function `main':
foo.c:(.text.startup+0x25): warning: the `gets' function is dangerous and should not be used.

自豪的采用jd5进行评测(github.com/masnn/jd5)

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