using System;

​

Public Class Form1 Private Sub Button1_Click(ByVal sender As System .Object, ByVal e As System .EventArgs)Handles btnConvert.Click If (IsNumeric (txtUsd.Text)  = 

False )Then lblError.Visible  =  True ElseIf (String.IsNullOrEmpty (txtUsd.Text) )

Then lblError.Visible  =  True Else lblError.Visible = False txtEur.Text = txtUsd.Text * 0.72387 End If End Sub End Class Public Class Form1 Private Sub Button1_Click (ByVal sender As System .Object, ByVal e As System .EventArgs)Handles btnConvert.Click If (IsNumeric (txtUsd.Text)  = 

False )Then lblError.Visible  =  True ElseIf (String.IsNullOrEmpty (txtUsd.Text) )

Then lblError.Visible  =  True Else lblError.Visible = False txtEur.Text = txtUsd.Text * 0.72387 End If End Sub End Class