In this example, we connect to a MongoDB server running on the local machine, build a BSON object with one field `"greeting"` and value `"hello"`, and insert it into the `testcoll` collection in the `testdb` database. Another example:c++ auto builder = bsoncxx::builder::stream::array{}; builder.appendAs(42, bsoncxx::type::k_int32); builder.appendAs("world", bsoncxx::type::k_utf8); auto arr = builder << bsoncxx::builder::stream::finalize; ``` This example shows how to build a BSON array with two elements: the integer `42` and the string `"world"`. The elements are appended using `appendAs` with the specified BSON types (`k_int32` and `k_utf8`). In conclusion, by using the `BSONObjBuilder` class and its `appendAs` method, we can easily build BSON objects and arrays programmatically in C++. This functionality is part of the MongoDB C++ driver library.