This guide describes the use of GNAT, a compiler and software development toolset for the full Ada programming language. It documents the features of the compiler and tools, and explains how to use them to build Ada applications. GNAT implements Ada 95 and Ada 2005, and it may also be invoked in Ada 83 compatibility mode. By default, GNAT assumes Ada 2005, but you can override with a compiler switch (see Section 3.2.9 [Compiling Different Versions of Ada], page 66) to explicitly specify the language version. Throughout this manual, references to "Ada" without a year suffix apply to both the Ada 95 and Ada 2005 versions of the language.