diff --git a/datastruct/deque.c b/datastruct/deque.c
index 12e4393..efab106 100644
--- a/datastruct/deque.c
+++ b/datastruct/deque.c
@@ -5,7 +5,7 @@ bool deque_push_back(struct _deque* self, void* obj)
 {
     assert(self != NULL);
     assert(self->_head != NULL);
-    struct _deque_node* node = NULL;
+    struct _deque_node* front = NULL;
 
     // create a new object
     void* new_obj = (void*)malloc(self->_obj_size);
@@ -33,11 +33,11 @@ bool deque_push_back(struct _deque* self, void* obj)
     new_node->prev = self->_head->next; 
     new_node->next = self->_head->prev;
 
-    node = self->_head->next;
-    node->next = new_node;
+    front = self->_head->next;
+    front->next = new_node;
 
-    node = self->_head->prev;
-    node->prev = new_node;
+    front = self->_head->prev;
+    front->prev = new_node;
 
     self->_head->next = new_node;
 
@@ -52,7 +52,36 @@ bool deque_push_front(struct _deque* self, void* obj)
 
 bool deque_pop_back(struct _deque* self, void* obj)
 {
+    assert(self != NULL);
+    assert(self->_head != NULL);
+    struct _deque_node* node = NULL;
+    struct _deque_node* back = NULL;
 
+    if (self->empty(self))
+    {
+        return false;
+    }
+
+    if (obj != NULL)
+    {
+        memmove(obj, self->_head->next->obj, self->_obj_size);
+    }
+    back = self->_head->next;
+    self->_head->next = back->prev;
+
+    node = self->_head->prev;
+    node->prev = self->_head->next;
+
+    free(back->obj);
+    free(back);
+
+    self->_size -= 1;
+    if (self->empty(self))
+    {
+        self->_head->prev = NULL;
+        self->_head->next = NULL;
+    }
+    return true;
 }
 
 bool deque_pop_front(struct _deque* self, void* obj)
@@ -109,7 +138,11 @@ bool deque_remove(struct _deque* self, void* obj)
 
 bool deque_clear(struct _deque* self)
 {
-
+    while (!self->empty(self))
+    {
+        deque_pop_back(self, NULL);
+    }
+    return true;
 }
 
 bool deque_get(struct _deque* self, int index, void* obj)
diff --git a/datastruct/deque_test.c b/datastruct/deque_test.c
index 800ab0c..ecfb376 100644
--- a/datastruct/deque_test.c
+++ b/datastruct/deque_test.c
@@ -3,13 +3,13 @@
 
 static void print_num(void* obj)
 {
-	printf("(%2d )", *(int*)obj);
+	printf("(%2d ) ", *(int*)obj);
 }
 
 static void deque_test_num(void)
 {
 	uint32_t i = 0;
-	int data[] = { 0, 1,2,3,4,5,6,7,8,9,10 };
+	int data[] = { 1,2,3,4,5,6,7,8,9,10 };
 	int temp = 0;
 	uint32_t len = sizeof(data) / sizeof(data[0]);
 
@@ -19,7 +19,7 @@ static void deque_test_num(void)
 
 	printf("\n\n----- deque_test_num -----\n");
 
-	printf("----- push_back -----\n");
+	printf("----- after push_back -----\n");
 	for (i = 0; i < len; i++)
 	{
 		dq.push_back(&dq, &data[i]);
@@ -44,27 +44,45 @@ static void deque_test_num(void)
 		printf("----- empty -----\n");
 	}
 
-#if 0
-	printf("----- pop -----\n");
+	printf("----- push_back -----\n");
+	for (i = 0; i < len; i++)
+	{
+		dq.push_back(&dq, &data[i]);
+	}
+
+	printf("----- after pop_back -----\n");
 	for (i = 0; i < len + 1; i++)
 	{
-		if (true == s.pop(&s, &temp))
+		if (true == dq.pop_back(&dq, &temp))
 		{
-			printf("top = ");
-			s.print_obj(&temp);
-			printf("\tsize after push = %2d\n", s.size(&s));
+			printf("pop = ");
+			dq.print_obj(&temp);
+
+			if (true == dq.front(&dq, &temp))
+			{
+				printf("front = ");
+				dq.print_obj(&temp);
+			}
+
+			if (dq.back(&dq, &temp))
+			{
+				printf("back = ");
+				dq.print_obj(&temp);
+			}
+
+			printf("size = %2d\n", dq.size(&dq));
 		}
 		else
 		{
 			printf("pop failed! because stack is empty\n");
 		}
 
-		if (s.empty(&s))
+		if (dq.empty(&dq))
 		{
 			printf("----- empty -----\n");
 		}
 	}
-#endif
+
 	dq.destory(&dq);
 }
 
diff --git a/datastruct/stack_test.c b/datastruct/stack_test.c
index 7b4a1af..0d91ac2 100644
--- a/datastruct/stack_test.c
+++ b/datastruct/stack_test.c
@@ -2,7 +2,7 @@
 
 static void print_num(void* obj)
 {
-	printf("(%2d )", *(int*)obj);
+	printf("(%2d ) ", *(int*)obj);
 }
 
 static void stack_test_num(void)
@@ -29,7 +29,8 @@ static void stack_test_num(void)
 
 		printf("top = ");
 		s.print_obj(&temp);
-		printf("\tsize after push = %2d\n", s.size(&s));
+
+		printf("size = %2d\n", s.size(&s));
 	}
 	printf("----- print -----\n");
 	s.print(&s);
@@ -40,9 +41,16 @@ static void stack_test_num(void)
 	{
 		if (true == s.pop(&s, &temp))
 		{
-			printf("top = ");
+			printf("pop = ");
 			s.print_obj(&temp);
-			printf("\tsize after push = %2d\n", s.size(&s));
+
+			if (s.peek(&s, &temp))
+			{
+				printf("top = ");
+				s.print_obj(&temp);
+			}
+
+			printf("size = %2d\n", s.size(&s));
 		}
 		else
 		{
@@ -60,7 +68,7 @@ static void stack_test_num(void)
 
 static void print_char(void* obj)
 {
-	printf("(%2c )", *(char*)obj);
+	printf("(%2c ) ", *(char*)obj);
 }
 
 static void stack_test_char(void)
@@ -86,7 +94,8 @@ static void stack_test_char(void)
 		s.peek(&s, &temp);
 		printf("top = ");
 		s.print_obj(&temp);
-		printf("\tsize after push = %2d\n", s.size(&s));
+
+		printf("size = %2d\n", s.size(&s));
 	}
 	printf("----- print -----\n");
 	s.print(&s);
@@ -97,9 +106,16 @@ static void stack_test_char(void)
 	{
 		if (true == s.pop(&s, &temp))
 		{
-			printf("top = ");
+			printf("pop = ");
 			s.print_obj(&temp);
-			printf("\tsize after push = %2d\n", s.size(&s));
+
+			if (s.peek(&s, &temp))
+			{
+				printf("top = ");
+				s.print_obj(&temp);
+			}
+
+			printf("size = %2d\n", s.size(&s));
 		}
 		else
 		{
@@ -154,7 +170,8 @@ static void stack_test_struct(void)
 		s.peek(&s, &temp);
 		printf("top = ");
 		s.print_obj(&temp);
-		printf("\tsize after push = %2d\n", s.size(&s));
+
+		printf("size = %2d\n", s.size(&s));
 	}
 	printf("----- print -----\n");
 	s.print(&s);
@@ -177,9 +194,16 @@ static void stack_test_struct(void)
 	{
 		if (true == s.pop(&s, &temp))
 		{
-			printf("top = ");
+			printf("pop = ");
 			s.print_obj(&temp);
-			printf("\tsize after push = %2d\n", s.size(&s));
+
+			if (s.peek(&s, &temp))
+			{
+				printf("top = ");
+				s.print_obj(&temp);
+			}
+
+			printf("size = %2d\n", s.size(&s));
 		}
 		else
 		{