add dynamic memory management

clang.md

@@ -384,6 +384,75 @@ int main(void)
 } 
 ```
 
+### Dynamic Memory Allocation
+
+C supports function for heap management:
+
+- `malloc`: allocate a block of **uninitialized** memory
+- `calloc`: allocate a block of **zeroed** memory
+- `free`: free previously allocated block of memory
+- `realloc`: change size of previously allocated block (**careful** - it might move!)
+
+The following is an example of binary tree implementation using dynamic memory allocation:
+
+```c
+#include <stdio.h>
+#include <stdlib.h>
+
+struct TreeNode {
+  int val;
+  struct TreeNode* left;
+  struct TreeNode* right;
+};
+
+struct TreeNode* create_node(int val) {
+  struct TreeNode* node = (struct TreeNode*) malloc(sizeof(struct TreeNode));
+  node->val = val;
+  node->left = NULL;
+  node->right = NULL;
+  return node;
+}
+
+// Traverse the tree in-order and print the values
+void traverse(struct TreeNode* node) {
+  if (node == NULL) {
+    return;
+  }
+  traverse(node->left);
+  printf("%d ", node->val);
+  traverse(node->right);
+}
+
+
+struct TreeNode* insert(struct TreeNode* root, int val) {
+  if (root == NULL) {
+    return create_node(val);
+  }
+  if (val < root->val) {
+    root->left = insert(root->left, val);
+  } else {
+    root->right = insert(root->right, val);
+  }
+  return root;
+}
+
+int main() {
+  struct TreeNode* root = NULL;
+  root = insert(root, 5);
+  root = insert(root, 3);
+  root = insert(root, 7);
+  root = insert(root, 2);
+  root = insert(root, 4);
+  root = insert(root, 6);
+  root = insert(root, 8);
+  traverse(root);
+  return 0;
+}
+```
+
+> There is a problem for this program, can you find out?
+
+
 ## C Compilation Process
 
 Unlike other interpreted programming languages, we use compilers to compile C written programs.