def command_check():
global is_on
if command == "view":
view()
is_on = False
elif command == "viewAll":
viewAll()
is_on = False
elif command == "num":
num()
is_on = False
elif command == "add":
add()
is_on = False
elif command == "change":
change()
is_on = False
elif command == "del":
delet()
is_on = False
elif command == "search":
search()
is_on = False
elif command == "exit":
exit()
else:
print("Ошибка. Несуществующая команда.")