Compilare: user.cpp: In function ‘int main()’: user.cpp:53:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ; i < strlen(s); ++ i) ^ user.cpp:58:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ; i < strlen(s); ) ^ user.cpp:83:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < strlen(s) && '0' <= s[i] && s[i] <= '9') ^