title: c# possible to check if a var is defined?
body: <p>I have a question: I need to check if a variable is defined in C#. I don't want to check if it is null because then I want to make this, it must exist.</p>
  <p>e.g. I need to know it the variable <code>string foo</code> is defined. Is there anything like:</p>
  <pre><code>isDefined(&quot;foo&quot;) :: bool
  </code></pre>