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copied!<p><code>var</code> is a <a href="http://msdn.microsoft.com/en-us/library/the35c6y.aspx" rel="nofollow noreferrer"><em>contextual keyword</em></a> - along with <code>yield</code>, <code>add</code> and <code>get</code> for example.</p> <p>In other words, you can use it as an identifer without prefixing it with @, but it still has a special meaning to the compiler in some places (i.e. where a type name is expected for a local variable declaration).</p> <p>Using <code>var</code> to declare a local variable asks the compiler to <em>infer</em> the type of the variable based on the expression on the right hand side. For example:</p> <pre><code>var list = new List<string>(); var anon = new { Foo = "bar" }; </code></pre> <p>The type of <code>list</code> is <code>List<string></code>; the type of <code>anon</code> is an <em>anonymous type</em>, also introduced in C# 3. Part of the reason for introducing <code>var</code> in C# 3 was to allow for strongly typed variables using anonymous types - the variable still has the appropriate compile-time type, even though you couldn't explicitly state that type.</p> <p>There are a few cases where <code>var</code> doesn't work, however, if the compiler doesn't have enough information:</p> <pre><code>var cantUseNull = null; var cantUseLambda = x => x.Length; </code></pre> <p>There are others too. In each case you <em>could</em> just cast the expression on the right-hand side, so that the compiler knew what to use - but in that case you might as well just declare the variable explicitly instead.</p> <p><code><plug></code><br> You can read more about this in <a href="http://manning.com/skeet2" rel="nofollow noreferrer">C# in Depth</a>. Fortunately, the chapter covering this is still available for free from the <a href="http://manning.com/skeet" rel="nofollow noreferrer">first edition page</a> (you want chapter 8). I can't remember how much I've changed this chapter in the second edition...<br> <code></plug></code></p>

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