/in/foo.cc: In function 'void Char()':
/in/foo.cc:10:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s.size();i++)
              ~^~~~~~~~~
/in/foo.cc:13:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(;j<t.size();j++)
        ~^~~~~~~~~
/in/foo.cc:20:7: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(j==t.size())
      ~^~~~~~~~~~