Compilare: user.cpp: In function ‘bool check(std::string)’: user.cpp:26:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size();++i) ^ user.cpp: In function ‘void add(std::string&, int, trie*)’: user.cpp:34:17: 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:35:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (j != a.size())if (p < 97 || p>122) return; ^ user.cpp:36:18: 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:51:16: 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:55:23: 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:65:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (j == a.size()){ ^