title: Using c# System.DateTime like c++ time_t
body: <p>In C++ I am able to get the current time when my application starts I can use</p>
  
  <pre><code>time_t appStartTime = time(null);
  </code></pre>
  
  <p>then to find the difference in seconds from when it started I can just do the same thing, then find the difference. It looks like I should be using "System.DateTime" in C# net, but the MSDN is confusing in its explanation.</p>
  
  <p>How can I use System.DateTime to find the difference in time (in seconds) between when my application starts, and the current time?</p>