Compilare: user.cpp: In function ‘std::string addd(std::string, std::string)’: user.cpp:20:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<x.size(); i++,q/=10) ^ user.cpp: In function ‘std::string sxi(std::string, int)’: user.cpp:37:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<x.size(); i++,q/=10) ^ user.cpp: In function ‘std::string zero(std::string)’: user.cpp:63:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; i<x.size(); i++) ^ user.cpp: In function ‘std::string multiply(std::string, std::string)’: user.cpp:74:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<y.size(); i++) ^ user.cpp: At global scope: user.cpp:94:6: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] main() ^