/in/foo.cc: In function 'bool pd()':
/in/foo.cc:89:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if(spn<st.size()) return true;
     ~~~^~~~~~~~~~
/in/foo.cc:90:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  else if(spn>st.size()) return false;
          ~~~^~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:103:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=1;i<=st.size();i++)
          ~^~~~~~~~~~~