/in/foo.cc: In function 'int main()':
/in/foo.cc:15:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<n;i++){
          ~^~
/in/foo.cc:16:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(j=0;j<a[i];j++){
           ~^~~~~
/in/foo.cc:17:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(k=0;k<a[i];k++)
            ~^~~~~