Public Function ValueIsIn(Of T As IComparable)(ByVal value As T, ByVal _
     ParamArray array() As T) As Boolean
      For Each element In array
         If element.CompareTo(value) = 0 Then Return True
      Next
 
      Return False
   End Function

      Dim int As Integer
 
      Integer.TryParse(TextBox1.Text, int)
 
      If ValueIsIn(int, 1, 2, 3, 4, 5) Then
         MessageBox.Show("vorhanden")
      Else
         MessageBox.Show("nicht vorhanden")
      End If