Compilare: user.cpp: In function ‘void add_hash(const string&)’: user.cpp:17:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<pat.size(); ++i) { ^ user.cpp: In function ‘bool check_hash(const string&)’: user.cpp:37:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<pat.size(); ++i) { ^