minor fixes

examples/widgets/checkbox/lv_example_checkbox_1.c

@@ -1,13 +1,12 @@
 #include "../../../lvgl.h"
-#include <stdio.h>
-#if LV_USE_CHECKBOX
+#if LV_USE_CHECKBOX && LV_BUILD_EXAMPLES
 
 static void event_handler(lv_obj_t * obj, lv_event_t event)
 {
     if(event == LV_EVENT_VALUE_CHANGED) {
         const char * txt = lv_checkbox_get_text(obj);
         const char * state = lv_obj_get_state(obj) & LV_STATE_CHECKED ? "Checked" : "Unchecked";
-        printf("%s: %s\n", txt, state);
+        LV_LOG_USER("%s: %s\n", txt, state);
     }
 }