Option Strict On
Option Explicit On
Module DoDemo

    Sub Main()
      Const PI As Double = 3.14159
      Dim radius As Double, area As Double

      Do 
        radius = Cdbl(InputBox("Type radius"))
        If radius < 0 Then
          Exit Do
        End If
        area = PI * radius * radius 
        Console.WriteLine(area)
      Loop

    End Sub
End Module