Compilare: user.cpp: In function 'std::string next(int, int)': user.cpp:34: warning: comparison between signed and unsigned integer expressions user.cpp: In function 'std::string inverse(int, int)': user.cpp:43: warning: comparison between signed and unsigned integer expressions user.cpp: In function 'int main()': user.cpp:68: warning: comparison between signed and unsigned integer expressions user.cpp:99: warning: comparison between signed and unsigned integer expressions