/in/foo.cc: In function 'int main()':
/in/foo.cc:9:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0;i<a.size();i++)
                     ~^~~~~~~~~
/in/foo.cc:10:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for(int j=0;j<b.size();j++)
                         ~^~~~~~~~~