VB.NET
* Public Class Form1

Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click

Dim zzTemp As String = Mid(TextBox1.Text, 1, 1)

If (Asc(zzTemp) >= 65 And Asc(zzTemp) <= 90) Or (Asc(zzTemp) >= 97 And Asc(zzTemp) <= 122) Then

MsgBox("ok")

Else

MsgBox("err")

End If

End Sub

End Class 

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