Compilare: user.cpp: In function ‘int get_num(const string&, int&)’: user.cpp:20:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( ; x < str.size() && isdigit(str[x]); ++x){ ^ user.cpp: In function ‘void tokenize(const string&, std::vector<int>&)’: user.cpp:25:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < str.size(); ){ ^ user.cpp: In function ‘void mk_polish(const std::vector<int>&, std::vector<int>&)’: user.cpp:51:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < v.size(); ++i){ ^ user.cpp: In function ‘int priority(int)’: user.cpp:16:15: warning: control reaches end of non-void function [-Wreturn-type] return 2; } } ^