foo.cc: In function 'void sc(char*)':
foo.cc:10:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<strlen(a);i++)
              ~^~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:22:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s1);
  ^~~~
In file included from /usr/include/c++/6/cstdio:42:0,
                 from foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
foo.cc:22:9: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s1);
         ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 from foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
foo.cc:23:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s2);
  ^~~~
In file included from /usr/include/c++/6/cstdio:42:0,
                 from foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
foo.cc:23:9: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s2);
         ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 from foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/tmp/ccjFAS6i.o: In function `main':
foo.cc:(.text.startup+0xc): 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)