/in/foo.cc: In function 'int main()':
/in/foo.cc:7:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<n.size();i++){
              ~^~~~~~~~~
/in/foo.cc:9:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  }for(int i=0;i<a.size();i++){
               ~^~~~~~~~~
/in/foo.cc:12:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<n.size();i++){
              ~^~~~~~~~~
/in/foo.cc:13:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=0;j<a.size();j++){
               ~^~~~~~~~~