Compilare: user.cpp: In function ‘bool cmp(std::string, std::string)’: user.cpp:33:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<a.size();++i) ^ user.cpp:35:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<b.size();++i) ^ user.cpp:40:13: warning: variable ‘a_’ set but not used [-Wunused-but-set-variable] int a_=0,b_=0; ^ user.cpp:40:18: warning: variable ‘b_’ set but not used [-Wunused-but-set-variable] int a_=0,b_=0; ^ user.cpp: In function ‘void query(std::string)’: user.cpp:96:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<a.size();++i) ^ user.cpp: In function ‘int main()’: user.cpp:162:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<x.size();++j) ^