Improve C++ example

--
MOS_MIGRATED_REVID=87514947

base_workspace/examples/cpp/hello-world.cc

diff --git a/base_workspace/examples/cpp/hello-world.cc b/base_workspace/examples/cpp/hello-world.cc
index 305b17f..be435c3 100644
--- a/base_workspace/examples/cpp/hello-world.cc
+++ b/base_workspace/examples/cpp/hello-world.cc
@@ -1,11 +1,26 @@
 #include "examples/cpp/hello-lib.h"
 
-int main(int argc, char** argv) {
-  const char* obj = "world";
-  if (argc > 1) {
-    obj = argv[1];
-  }
+#include <string>
 
-  greet(obj);
+using hello::HelloLib;
+using std::string;
+
+/**
+ * This prints "Hello world". If it is run with arguments, it will use the first
+ * argument instead of "world". Build and run //examples/cpp:hello-world to see
+ * this program in action.
+ *
+ * This file does double-duty as a "test." It is a cc_binary, so it can also be
+ * compiled as a cc_test and Bazel will decide on whether it passed or failed
+ * based on exit code (which is always 0 here, so the test "passes"). See
+ * hello-fail.cc for an example of making a test fail.
+ */
+int main(int argc, char** argv) {
+  HelloLib lib("Hello");
+  string thing = "world";
+  if (argc > 1) {
+    thing = argv[1];
+  }
+  lib.greet(thing);
   return 0;
 }