title: Fastest way to check if string contains only digits in C#
body: <p>I know a few ways of how to check if a string contains only digits:<br />
  RegEx, <code>int.parse</code>, <code>tryparse</code>, looping, etc.</p>
  <p>Can anyone tell me what the <em>fastest</em> way to check is?</p>
  <p>I need only to <strong>CHECK</strong> the value, no need to actually parse it.</p>
  <p>By &quot;digit&quot; I mean specifically ASCII digits: <code>0 1 2 3 4 5 6 7 8 9</code>.</p>
  <p>This is not the same question as <a href="https://stackoverflow.com/questions/894263/how-do-i-identify-if-a-string-is-a-number">Identify if a string is a number</a>, since this question is not only about how to identify, but also about what the <strong>fastest</strong> method for doing so is.</p>