/in/foo.cc: In function 'int main()':
/in/foo.cc:39:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int l=0;l<st.size();l++)
               ~^~~~~~~~~~
/in/foo.cc:42:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int r=0;r<st.size();r++)
                ~^~~~~~~~~~
/in/foo.cc:60:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<st.size();i++)
               ~^~~~~~~~~~