/in/foo.cc: In function 'void work()':
/in/foo.cc:16:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<v[fx].size();i++){
                 ~^~~~~~~~~~~~~
/in/foo.cc:21:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<v[fx].size();i++) c[v[fx][i]] = fy;
                 ~^~~~~~~~~~~~~