error codes are values that identify different types of errors in the Windows API. Most functions do not report the error code directly; instead, they simply return a flag specifying if some error occured or not.
these are samples, not complete applications. The code (and coding style) is not meant to be industrial strength; it's not even well-designed. The sole purpose of the samples is illustrating a point, not teaching proper coding style.
Speech for Windows® applications, includes freely distributable text-to-speech engines (in U.S. English and Simplified Chinese) and speech recognition engines (in U.S. English, Simplified Chinese, and Japanese).