foo.cc: In function 'int main()':
foo.cc:10:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(a);
  ^~~~
In file included from foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
foo.cc:10:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(a);
        ^
In file included from foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/tmp/cczXd3zb.o: In function `main':
foo.cc:(.text.startup+0x16): 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)