/in/foo.cc: In function 'int main()':
/in/foo.cc:12:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int k=0;k<x[j].size();k++){
                ^
/in/foo.cc:13:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(k<x[j].size()-1)
        ^