diff --git a/c-programming/strings/str_replace.h b/c-programming/strings/str_replace.h
index 55de70f..60b5201 100644
--- a/c-programming/strings/str_replace.h
+++ b/c-programming/strings/str_replace.h
@@ -16,6 +16,9 @@
 // : parameters
 // : : count of replacements
 #define STR_REPLACE_ALL 0
+// : : directions
+#define STR_REPLACE_DIR_FORWARD false
+#define STR_REPLACE_DIR_BACKWARD true
 
 // function definitions
 char* str_replace(