Compilare: main.cpp: In function 'bool query(std::__cxx11::string)': main.cpp:16:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<bt.size(); i++) ~^~~~~~~~~~ main.cpp:21:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0; j<op[i].size(); j++) { ~^~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:53:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0; j<op[i].size(); j++) { ~^~~~~~~~~~~~~