Compilare: user.cpp: In function ‘int main()’: user.cpp:63:12: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] check[k] = NULL; ^ user.cpp:64:29: warning: NULL used in arithmetic [-Wpointer-arith] for (itc = check; *itc != NULL; itc++) ^ user.cpp:70:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < p->v.size(); i++) ^