diff --git a/HW2_three files/README.md b/HW2_three files/README.md
index c94effacf6b78a1fabfb2411294f90a3c54ae30a..2628fa0756e427122301b314165962f008808584 100644
--- a/HW2_three files/README.md	
+++ b/HW2_three files/README.md	
@@ -20,4 +20,5 @@
 #GCC compile -- by using preprocessor
 - #ifdef, #else, #endif
     -- func.c에서 int func_name_or_id() 구현 (no using #define PRINT_ID)
-    -- difference between gcc -DPRINT_ID main.c func.c and gcc main.c func.c
\ No newline at end of file
+    -- difference between gcc -DPRINT_ID main.c func.c and gcc main.c func.c
+    -- gcc -DPRINT_ID는 PRINT_ID가 정의된 상태로 컴파일 되므로 #ifdef 실행
\ No newline at end of file