Compilare: user.cpp: In function ‘void back(int)’: user.cpp:24: warning: suggest explicit braces to avoid ambiguous ‘else’ user.cpp: In function ‘int main()’: user.cpp:35: warning: unused variable ‘j’ user.cpp: In function ‘int valid(int)’: user.cpp:18: warning: control reaches end of non-void function user.cpp: In function ‘int main()’: user.cpp:38: warning: array subscript is above array bounds