Add freetree() and freelist().

freetree and freelist free the allocated heap memory manually rather
than relying on the OS for garbage collection. This avoid potential
memory leak issues, which is good practice.

Author: fsaadatmand

chapter06/6-3.c

@@ -52,6 +52,8 @@ struct tnode *addtree(struct tnode *, char *, int);
 void   treeprint(struct tnode *);
 void   printList(struct list *);
 struct key *binsearch(char *, struct key *, int);
+struct tnode *freetree(struct tnode *);
+struct list *freelist(struct list *);
 
 /* globals */
 char   buf[BUFSIZE];                   /* buffer from ungetch */
@@ -188,6 +190,29 @@ struct key *binsearch(char *word, struct key *tab, int n)
 	return NULL;
 }
 
+/* freellist: frees allocated heap memory of linked list */
+struct list *freelist(struct list *node)
+{
+	if (node->next != NULL) {
+		freelist(node->next);
+		free(node);
+	}
+	return node;
+}
+
+/* freetree: frees allocated heap memory of tree */
+struct tnode *freetree(struct tnode *node)
+{
+	if (node != NULL) {
+		freetree(node->left);
+		freetree(node->right);
+		free(node->word);
+		freelist(node->line);          /* delete linked list nodes */
+		free(node->line);              /* delete linked list */
+		free(node);
+	}
+	return node;
+}
 int main(void)
 {
 	struct tnode *root;                /* root node */
@@ -206,5 +231,6 @@ int main(void)
 			root = addtree(root, word, lineNumb);
 	}
 	treeprint(root);
+	root = freetree(root);             /* clean up */
 	return 0;
 }