diff --git a/README.md b/README.md
index ed6d442..76c9cf3 100644
--- a/README.md
+++ b/README.md
@@ -187,15 +187,21 @@ int main() {
     keys.erase(std::unique(keys.begin(), keys.end()), keys.end());
 
     // The trie dictionary type
-    using trie_type = xcdat::trie_8_type;
+    using trie_type = xcdat::trie_7_type;
+    // using trie_type = xcdat::trie_8_type;
+    // using trie_type = xcdat::trie_15_type;
+    // using trie_type = xcdat::trie_16_type;
 
     // The dictionary filename
     const char* tmp_filename = "dic.bin";
 
     // Build and save the trie dictionary.
-    {
+    try {
         const trie_type trie(keys);
         xcdat::save(trie, tmp_filename);
+    } catch (const xcdat::exception& ex) {
+        std::cerr << ex.what() << std::endl;
+        return 1;
     }
 
     // Load the trie dictionary on memory.
@@ -300,7 +306,7 @@ Enumerate() = {
 
 ## API
 
-Xcdat can be used by including only the header `xcdat.hpp`.
+Xcdat consists of only the header files and can be used by including only the header `xcdat.hpp`. Also, it uses `namespace xcdat`.
 
 ### Trie dictionary types
 
@@ -322,7 +328,7 @@ using trie_15_type = trie<bc_vector_15>;
 
 ### Trie dictionary class
 
-The trie dictionary has the following members.
+The trie dictionary class provides the following functions.
 
 ```c++
 //! A compressed string dictionary based on an improved double-array trie.
diff --git a/sample/sample.cpp b/sample/sample.cpp
index c6788e4..0c181c5 100644
--- a/sample/sample.cpp
+++ b/sample/sample.cpp
@@ -15,15 +15,21 @@ int main() {
     keys.erase(std::unique(keys.begin(), keys.end()), keys.end());
 
     // The trie dictionary type
-    using trie_type = xcdat::trie_8_type;
+    using trie_type = xcdat::trie_7_type;
+    // using trie_type = xcdat::trie_8_type;
+    // using trie_type = xcdat::trie_15_type;
+    // using trie_type = xcdat::trie_16_type;
 
     // The dictionary filename
     const char* tmp_filename = "dic.bin";
 
     // Build and save the trie dictionary.
-    {
+    try {
         const trie_type trie(keys);
         xcdat::save(trie, tmp_filename);
+    } catch (const xcdat::exception& ex) {
+        std::cerr << ex.what() << std::endl;
+        return 1;
     }
 
     // Load the trie dictionary on memory.