/in/foo.cc: In function 'int main()':
/in/foo.cc:17:11: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     while(gets(tmp)!=NULL){
           ^
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:5249,
                 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 /in/foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^
/in/foo.cc:17:11: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     while(gets(tmp)!=NULL){
           ^
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:5249,
                 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 /in/foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^
/in/foo.cc:17:19: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     while(gets(tmp)!=NULL){
                   ^
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:5249,
                 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 /in/foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^
/in/foo.cc:19:17: error: 'strrev' was not declared in this scope
         strrev(a);
                 ^
/in/foo.cc:24:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0;i<s.size();i++)
              ^