Compilare: user.cpp: In function ‘int valid(int)’: user.cpp:20:9: warning: unused variable ‘i’ [-Wunused-variable] int i, j, ev=1; ^ user.cpp:20:12: warning: unused variable ‘j’ [-Wunused-variable] int i, j, ev=1; ^ user.cpp: In function ‘void back()’: user.cpp:49:19: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if(valid(k)) ^