参考答案

Private Sub Command1_Click()
    Dim tmpStr As String * 50
    Select Case Form1.Combo1.ListIndex
        Case 0
            tmpStr = Left(Trim(Text1.Text), 3)
        Case 1
            tmpStr = Right(Trim(Text1.Text), 3)
        Case 2
            tmpStr = Mid(Trim(Text1.Text), 3, 4)
    End Select
    Text2.Text = tmpStr
End Sub