Compilare: user.cpp: In function ‘void add(std::string&, std::string)’: user.cpp:247:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0;i<s1.length()-1;i++) ^ user.cpp:203:9: warning: unused variable ‘firstNr’ [-Wunused-variable] int firstNr = getInt(s1.at(0)); ^ user.cpp: In function ‘std::string getString(int)’: user.cpp:48:1: warning: control reaches end of non-void function [-Wreturn-type] } ^