/in/foo.cc: In function 'int main()':
/in/foo.cc:19:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(;i<str.size();i++)
        ~^~~~~~~~~~~
/in/foo.cc:35:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(sum==0&&i==str.size()) cout<<"Case #"<<k<<": YES"<<endl;
              ~^~~~~~~~~~~~
/in/foo.cc:36:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   else if(i<str.size())
           ~^~~~~~~~~~~
/in/foo.cc:39:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(;i<str.size();i++)
         ~^~~~~~~~~~~
/in/foo.cc:44:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   else if(i==str.size()&&flag) cout<<"Case #"<<k<<": YES"<<endl;
           ~^~~~~~~~~~~~