Compilare: user.cpp: In function ‘void add(std::string&, int, trie*)’: user.cpp:27:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (j < a.size()) p = a[j]<97 ? a[j]+32 : a[j]; ^ user.cpp:28:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (j == a.size()){ ^ user.cpp: In function ‘std::string tip(std::string&, int, trie*)’: user.cpp:45:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (j< a.size() && !c->childs[p - 'a']) return "Search Bing for " + a; ^ user.cpp:49:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] else if (j == a.size()){ ^ user.cpp: In function ‘void ModRel(std::string&, const int&, int, trie*)’: user.cpp:59:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (j == a.size()){ ^