Compilare: main.cpp: In function 'int main()': main.cpp:47:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(k = 1; k < ret[j + 1].size() and ok; k++) ~~^~~~~~~~~~~~~~~~~~~ main.cpp:53:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(!ok or f.count() != n) ~~~~~~~~~~^~~~ main.cpp:59:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(k = 1; k < ret[j + 1].size(); k++) ~~^~~~~~~~~~~~~~~~~~~