Tab control(vb.net 2008)

currenttab = 0 ' Start with first tab
currenttab = TabControl1.SelectedIndex
        currenttab = currenttab + 1
        If (currenttab < TabControl1.TabCount) Then

            TabControl1.SelectedIndex = currenttab

        End If



currenttab = TabControl1.SelectedIndex
        currenttab = currenttab - 1
        If (currenttab > -1) Then

            TabControl1.SelectedIndex = currenttab

        End If

        If currenttab = 0 Then
            Button1.Enabled = False
        ElseIf currenttab > 0 Then
            Button1.Enabled = True
        End If