/in/foo.cc: In function 'int main()':
/in/foo.cc:31:5: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     gets(s1);
     ^~~~
In file included from /in/foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:31:12: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     gets(s1);
            ^
In file included from /in/foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:32:5: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     gets(s2);
     ^~~~
In file included from /in/foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:32:12: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     gets(s2);
            ^
In file included from /in/foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:33:28: error: 'Diff' was not declared in this scope
     printf("%d %d", Diff(s1), Diff(s2));
                            ^