diff --git a/050_pow/pow.c b/050_pow/pow.c
index 5f00361..68c9fa9 100644
--- a/050_pow/pow.c
+++ b/050_pow/pow.c
@@ -41,6 +41,10 @@ static double my_pow(double x, int n)
 
 int main(int argc, char **argv)
 {
+    if (argc != 3) {
+        fprintf(stderr, "Usage: ./test x n\n");
+        exit(-1);
+    }
     printf("%lf\n", my_pow(atoi(argv[1]), atoi(argv[2])));
     return 0;
 }
diff --git a/101_symmetric_tree/Makefile b/101_symmetric_tree/Makefile
new file mode 100644
index 0000000..eb640cf
--- /dev/null
+++ b/101_symmetric_tree/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test symmetric_tree.c
diff --git a/101_symmetric_tree/symmetric_tree.c b/101_symmetric_tree/symmetric_tree.c
new file mode 100644
index 0000000..4a0809d
--- /dev/null
+++ b/101_symmetric_tree/symmetric_tree.c
@@ -0,0 +1,83 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+struct TreeNode {
+    int val;
+    struct TreeNode *left;
+    struct TreeNode *right;
+};
+
+static bool traverse(struct TreeNode *left, struct TreeNode *right)
+{
+    if (left == NULL && right == NULL) {
+        return true;
+    }
+
+    if (left == NULL || right == NULL) {
+        return false;
+    }
+
+    if (left->val != right->val) {
+        return false;
+    }
+
+    return traverse(left->left, right->right) && traverse(left->right, right->left);
+}
+
+bool isSymmetricTree(struct TreeNode* root)
+{
+    if (root == NULL) {
+        return true;
+    }
+
+    return traverse(root->left, root->right);
+}
+
+int main(void)
+{
+#if 1
+    struct TreeNode root, n10, n11, n20, n21, n22, n23;
+    root.val = 1;
+    n10.val = 2;
+    n11.val = 2;
+    n20.val = 3;
+    n21.val = 4;
+    n22.val = 4;
+    n23.val = 3;
+    root.left = &n10;
+    root.right = &n11;
+    n10.left = &n20;
+    n10.right = &n21;
+    n11.left = &n22;
+    n11.right = &n23;
+    n20.left = NULL;
+    n20.right = NULL;
+    n21.left = NULL;
+    n21.right = NULL;
+    n22.left = NULL;
+    n22.right = NULL;
+    n23.left = NULL;
+    n23.right = NULL;
+#else
+    struct TreeNode root, n10, n11, n21, n22;
+    root.val = 1;
+    n10.val = 2;
+    n11.val = 2;
+    n21.val = 3;
+    n22.val = 4;
+    root.left = &n10;
+    root.right = &n11;
+    n10.left = NULL;
+    n10.right = &n21;
+    n11.left = &n22;
+    n11.right = NULL;
+    n21.left = NULL;
+    n21.right = NULL;
+    n22.left = NULL;
+    n22.right = NULL;
+#endif
+
+    printf("%s\n", isSymmetricTree(&root) ? "true" : "false");
+    return 0;
+}