Compilare: user.cpp: In function 'int valid(long long int)': user.cpp:9: warning: comparison between signed and unsigned integer expressions user.cpp:16: warning: comparison between signed and unsigned integer expressions user.cpp:19: warning: comparison between signed and unsigned integer expressions user.cpp:7: warning: unused variable 'step' user.cpp:7: warning: unused variable 'i' user.cpp:7: warning: unused variable 'S' user.cpp:7: warning: unused variable 'D1' user.cpp: In function 'void cit()': user.cpp:57: warning: comparison between signed and unsigned integer expressions