title: Putting value from Combobox Item to Textbox in vb.net "Conversion from string "" to type 'Double' is not valid."
body: <pre><code>Public Class Main
      Dim Adult As Integer = 495 'Adult as Integer
      Dim Senior As Integer = 395 'Senior as Integer
  
      Private Sub Combo() 'New created Sub
          Dim Aval = Combad.Text 'Aval as Combo box Adult
          Dim Sval = Comse.Text 'Sval as Combo box Senior
  
  
          Textpay.Text = Adult * Aval + Senior * Sval 'Adding up the total of both Combo Box's Value
      End Sub
  Private Sub Combad_SelectedIndexChanged(sender As Object, e As EventArgs) Handles Combad.SelectedIndexChanged
          Combo() 'Private Sub
      End Sub
  
      Private Sub Comse_SelectedIndexChanged(sender As Object, e As EventArgs) Handles Comse.SelectedIndexChanged
          Combo() 'Private Sub
      End Sub
  End Class
  </code></pre>