diff --git a/lib/hcl.h b/lib/hcl.h
index 0c16c91..201237e 100644
--- a/lib/hcl.h
+++ b/lib/hcl.h
@@ -833,7 +833,8 @@ enum hcl_iocmd_t
 	HCL_IO_OPEN,
 	HCL_IO_CLOSE,
 	HCL_IO_READ,
-	HCL_IO_WRITE
+	HCL_IO_WRITE,
+	HCL_IO_FLUSH
 };
 typedef enum hcl_iocmd_t hcl_iocmd_t;
 
@@ -1620,6 +1621,9 @@ HCL_EXPORT void hcl_detachio (
 	hcl_t*       hcl
 );
 
+HCL_EXPORT void hcl_flushio (
+	hcl_t*       hcl
+);
 
 HCL_EXPORT hcl_oop_t hcl_read (
 	hcl_t*       hcl
diff --git a/lib/main.c b/lib/main.c
index dd59063..3b3a366 100644
--- a/lib/main.c
+++ b/lib/main.c
@@ -310,6 +310,10 @@ static int read_handler (hcl_t* hcl, hcl_iocmd_t cmd, void* arg)
 		case HCL_IO_READ:
 			return read_input (hcl, (hcl_ioinarg_t*)arg);
 
+		case HCL_IO_FLUSH:
+			/* no effect on an input stream */
+			return 0;
+
 		default:
 			hcl_seterrnum (hcl, HCL_EINTERN);
 			return -1;
@@ -390,18 +394,32 @@ static HCL_INLINE int write_output (hcl_t* hcl, hcl_iooutarg_t* arg)
 	return 0;
 }
 
+static HCL_INLINE int flush_output (hcl_t* hcl, hcl_iooutarg_t* arg)
+{
+	FILE* fp;
+
+	fp = (FILE*)arg->handle;
+	HCL_ASSERT (hcl, fp != HCL_NULL);
+
+	fflush (fp);
+	return 0;
+}
+
 static int print_handler (hcl_t* hcl, hcl_iocmd_t cmd, void* arg)
 {
 	switch (cmd)
 	{
 		case HCL_IO_OPEN:
-			return open_output (hcl, (hcl_iooutarg_t*)arg);
+			return open_output(hcl, (hcl_iooutarg_t*)arg);
 
 		case HCL_IO_CLOSE:
-			return close_output (hcl, (hcl_iooutarg_t*)arg);
+			return close_output(hcl, (hcl_iooutarg_t*)arg);
 
 		case HCL_IO_WRITE:
-			return write_output (hcl, (hcl_iooutarg_t*)arg);
+			return write_output(hcl, (hcl_iooutarg_t*)arg);
+
+		case HCL_IO_FLUSH:
+			return flush_output(hcl, (hcl_iooutarg_t*)arg);
 
 		default:
 			hcl_seterrnum (hcl, HCL_EINTERN);
@@ -1191,6 +1209,7 @@ count++;
 			}
 			else if (xtn->reader_istty)
 			{
+				/* interactive mode */
 				hcl_oop_t retv;
 
 				hcl_decode (hcl, code_offset, hcl_getbclen(hcl));
@@ -1199,6 +1218,10 @@ count++;
 				//setup_tick ();
 
 				retv = hcl_executefromip(hcl, code_offset);
+
+				/* flush pending output data in the interactive mode(e.g. printf without a newline) */
+				hcl_flushio (hcl); 
+
 				if (!retv)
 				{
 					hcl_logbfmt (hcl, HCL_LOG_STDERR, "ERROR: cannot execute - [%d] %js\n", hcl_geterrnum(hcl), hcl_geterrmsg(hcl));
diff --git a/lib/read.c b/lib/read.c
index f4ba8c1..27502ae 100644
--- a/lib/read.c
+++ b/lib/read.c
@@ -2298,10 +2298,10 @@ int hcl_attachio (hcl_t* hcl, hcl_ioimpl_t reader, hcl_ioimpl_t printer)
 		HCL_MEMSET (&cb, 0, HCL_SIZEOF(cb));
 		cb.gc = gc_compiler;
 		cb.fini = fini_compiler;
-		cbp = hcl_regcb (hcl, &cb);
+		cbp = hcl_regcb(hcl, &cb);
 		if (!cbp) return -1;
 
-		hcl->c = (hcl_compiler_t*)hcl_callocmem (hcl, HCL_SIZEOF(*hcl->c));
+		hcl->c = (hcl_compiler_t*)hcl_callocmem(hcl, HCL_SIZEOF(*hcl->c));
 		if (!hcl->c) 
 		{
 			hcl_deregcb (hcl, cbp);
@@ -2341,11 +2341,11 @@ int hcl_attachio (hcl_t* hcl, hcl_ioimpl_t reader, hcl_ioimpl_t printer)
 	hcl->c->inarg.colm = 1;
 
 	/* open the top-level stream */
-	n = hcl->c->reader (hcl, HCL_IO_OPEN, &hcl->c->inarg);
+	n = hcl->c->reader(hcl, HCL_IO_OPEN, &hcl->c->inarg);
 	if (n <= -1) goto oops;
 
 	HCL_MEMSET (&hcl->c->outarg, 0, HCL_SIZEOF(hcl->c->outarg));
-	n = hcl->c->printer (hcl, HCL_IO_OPEN, &hcl->c->outarg);
+	n = hcl->c->printer(hcl, HCL_IO_OPEN, &hcl->c->outarg);
 	if (n <= -1) 
 	{
 		hcl->c->reader (hcl, HCL_IO_CLOSE, &hcl->c->inarg);
@@ -2371,6 +2371,14 @@ oops:
 	return -1;
 }
 
+void hcl_flushio (hcl_t* hcl)
+{
+	if (hcl->c)
+	{
+		if (hcl->c->printer) hcl->c->printer (hcl, HCL_IO_FLUSH, &hcl->c->outarg);
+	}
+}
+
 void hcl_detachio (hcl_t* hcl)
 {
 	/* an error occurred and control has reached here