title: How to stop a process running more than once
body: <p>I'm working on a my Windows Forms application. I start a calculator process on a button click event using this code:</p>
  
  <pre><code>System.Diagnostics.Process.Start("calc.exe");
  </code></pre>
  
  <p>If I click the button again, another calculator process is started. So how do I stop the process from running more than once?</p>
  
  <p>Thanks</p>