Compilare: main.cpp: In function 'std::vector<std::__cxx11::basic_string<char> > preprocess(std::vector<std::__cxx11::basic_string<char> >&)': main.cpp:64:43: warning: NULL used in arithmetic [-Wpointer-arith] 64 | for(int k = 0; words[j][k] != NULL; ++k){ | ^~~~ main.cpp:71:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 71 | if(index == words[i].size()){ | ~~~~~~^~~~~~~~~~~~~~~~~~