title: Validate user input in a TextBox
body: <p>User provides value in <code>txtAmount</code> TextBox that I later process this way:</p>
  
  <pre><code>c = txtAmount.Text 'GET AN ERROR HERE BECAUSE I NEED C TO BE AN  INT
  </code></pre>
  
  <p>I want a user to be able to correct entered value, so I can get <code>c</code> as an integer:</p>
  
  <pre><code>If Not (IsNumeric(txtAmount.Text)) Then
    lblMsg.Caption = " Please enter you answer numericly "
    txtAmount.Text = ""
    txtAmount.SetFocus 'HERE IS WHAT I WANT TO FIX
  End If
  If (txtAmount.Text = "") Then
    lblMsg.Caption = " Please enter amount to convert"
    txtAmount.SetFocus
  End If
  </code></pre>
  
  <p>Where should I place my validation code so its called before I process entered value?</p>