/in/foo.cc: In function 'int main()':
/in/foo.cc:101:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j=0;j<a[i].size();j++){
                ~^~~~~~~~~~~~
/in/foo.cc:104:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
      for(int k=0;k<a[i].size();k++){
                  ~^~~~~~~~~~~~
/in/foo.cc:120:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j=0;j<a[i].size();j++){
                ~^~~~~~~~~~~~