Compilare: main.cpp: In function 'void trie_insert(std::__cxx11::string, int)': main.cpp:48:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<a.length(); i++) ~^~~~~~~~~~~ main.cpp: In function 'void trie_mark(std::__cxx11::string)': main.cpp:74:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<a.length(); i++) ~^~~~~~~~~~~ main.cpp: In function 'void read()': main.cpp:100:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int k=0; k<aux.length(); k++) ~^~~~~~~~~~~~~ main.cpp:111:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int k=0; k<aux.length(); k++) ~^~~~~~~~~~~~~