/in/foo.cc: In function 'void rever(int)':
/in/foo.cc:6:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if(pos==s1.size())
     ~~~^~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:14:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s.size()-1;i++)
              ~^~~~~~~~~~~