foo.cc: In function 'int main()':
foo.cc:8:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s);
  ^
In file included from /usr/include/c++/5/cstdio:42:0,
                 from /usr/include/c++/5/ext/string_conversions.h:43,
                 from /usr/include/c++/5/bits/basic_string.h:5352,
                 from /usr/include/c++/5/string:52,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^
foo.cc:8:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s);
  ^
In file included from /usr/include/c++/5/cstdio:42:0,
                 from /usr/include/c++/5/ext/string_conversions.h:43,
                 from /usr/include/c++/5/bits/basic_string.h:5352,
                 from /usr/include/c++/5/string:52,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^
foo.cc:8:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s);
        ^
In file included from /usr/include/c++/5/cstdio:42:0,
                 from /usr/include/c++/5/ext/string_conversions.h:43,
                 from /usr/include/c++/5/bits/basic_string.h:5352,
                 from /usr/include/c++/5/string:52,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^
foo.cc:9:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(t);
  ^
In file included from /usr/include/c++/5/cstdio:42:0,
                 from /usr/include/c++/5/ext/string_conversions.h:43,
                 from /usr/include/c++/5/bits/basic_string.h:5352,
                 from /usr/include/c++/5/string:52,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^
foo.cc:9:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(t);
  ^
In file included from /usr/include/c++/5/cstdio:42:0,
                 from /usr/include/c++/5/ext/string_conversions.h:43,
                 from /usr/include/c++/5/bits/basic_string.h:5352,
                 from /usr/include/c++/5/string:52,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^
foo.cc:9:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(t);
        ^
In file included from /usr/include/c++/5/cstdio:42:0,
                 from /usr/include/c++/5/ext/string_conversions.h:43,
                 from /usr/include/c++/5/bits/basic_string.h:5352,
                 from /usr/include/c++/5/string:52,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^
foo.cc:17:16: error: 'strlen' was not declared in this scope
   si=k+strlen(t);
                ^
foo.cc:8:9: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
  gets(s);
         ^
foo.cc:9:9: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
  gets(t);
         ^

自豪的采用 HydroJudger 进行评测(github.com/hydro-dev/HydroJudger)