title: Validating a Textbox field for only numeric input.
body: <p>I have created a form-based program that needs some input validation.  I need to make sure the user can only enter numeric values within the distance Textbox.</p>
  
  <p>So far, I've checked that the Textbox has something in it, but if it has a value then it should proceed to validate that the entered value is numeric:</p>
  
  <pre><code>else if (txtEvDistance.Text.Length == 0)
          {
              MessageBox.Show("Please enter the distance");
          }
  else if (cboAddEvent.Text //is numeric)
          {
              MessageBox.Show("Please enter a valid numeric distance");
          }
  </code></pre>