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copied!<p>Three things are being declared here: an anonymous enumerated type is declared, <code>ShapeType</code> is being declared a typedef for that anonymous enumeration, and the three names <code>kCircle</code>, <code>kRectangle</code>, and <code>kOblateSpheroid</code> are being declared as integral constants.</p> <p>Let's break that down. In the simplest case, an enumeration can be declared as</p> <pre><code>enum tagname { ... }; </code></pre> <p>This declares an enumeration with the tag <code>tagname</code>. In C and Objective-C (but <em>not</em> C++), any references to this <em>must</em> be preceded with the <code>enum</code> keyword. For example:</p> <pre><code>enum tagname x; // declare x of type 'enum tagname' tagname x; // ERROR in C/Objective-C, OK in C++ </code></pre> <p>In order to avoid having to use the <code>enum</code> keyword everywhere, a typedef can be created:</p> <pre><code>enum tagname { ... }; typedef enum tagname tagname; // declare 'tagname' as a typedef for 'enum tagname' </code></pre> <p>This can be simplified into one line:</p> <pre><code>typedef enum tagname { ... } tagname; // declare both 'enum tagname' and 'tagname' </code></pre> <p>And finally, if we don't need to be able to use <code>enum tagname</code> with the <code>enum</code> keyword, we can make the <code>enum</code> anonymous and only declare it with the typedef name:</p> <pre><code>typedef enum { ... } tagname; </code></pre> <p>Now, in this case, we're declaring <code>ShapeType</code> to be a typedef'ed name of an anonymous enumeration. <code>ShapeType</code> is really just an integral type, and should only be used to declare variables which hold one of the values listed in the declaration (that is, one of <code>kCircle</code>, <code>kRectangle</code>, and <code>kOblateSpheroid</code>). You can assign a <code>ShapeType</code> variable another value by casting, though, so you have to be careful when reading enum values.</p> <p>Finally, <code>kCircle</code>, <code>kRectangle</code>, and <code>kOblateSpheroid</code> are declared as integral constants in the global namespace. Since no specific values were specified, they get assigned to consecutive integers starting with 0, so <code>kCircle</code> is 0, <code>kRectangle</code> is 1, and <code>kOblateSpheroid</code> is 2.</p>

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