/in/foo.cc: In function 'int main()':
/in/foo.cc:8:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=j=0;i<s.size();i++)
            ~^~~~~~~~~
/in/foo.cc:10:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(j<s.size()&&sum<n)
         ~^~~~~~~~~
/in/foo.cc:15:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(j<s.size()&&s[j]=='1')
         ~^~~~~~~~~