Partial Class _Default
Inherits System.Web.UI.Page

Protected Sub TextBox1_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
Dim h, w As Single
h = Single.Parse(TextBox1.Text)
w = Single.Parse(TextBox2.Text)

Label3.Text = ((w / (h * h)) * 10000).ToString

If Label3.Text < 18.5 Then

Label4.Text = "やせ"

ElseIf 18.5 <= Label3.Text < 25 Then

Label4.Text = "標準"

ElseIf 25 <= Label3.Text < 30 Then

Label4.Text = "肥満"

Else

Label4.Text = "高度肥満"

End If


End Sub
End Class


うまくいきませんね。