/in/foo.cc: In function 'int main()':
/in/foo.cc:123:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int j=0;j<a_s[i].size();j++)
                          ~^~~~~~~~~~~~~~
/in/foo.cc:138:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int j=0;j<b_s[i].size();j++)
                          ~^~~~~~~~~~~~~~
/in/foo.cc:155:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int i=0;i<p_1_s.size();i++)
                          ~^~~~~~~~~~~~~
/in/foo.cc:161:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
                 for (int i=0;i<p_2_s.size();i++)
                              ~^~~~~~~~~~~~~