在VB中，字母以ASCII形式存儲，而大小寫字母的ASCII值相差32，這樣的話，如果一個大寫字母的ASCII值加上32就會變為對應的小寫字母，而小寫字母的ASCII值減去32就會變為大寫字母。在VB中實現大小寫轉換的源代碼如下：

'大寫字母轉小寫字母

Private Sub Text1_KeyPress(KeyAscii As Integer)
               If KeyAscii >= 65 And KeyAscii <= 90 Then
                    KeyAscii = KeyAscii + 32
               End If
        End Sub

'小寫字母轉大寫字母

Private Sub Text2_KeyPress(KeyAscii As Integer)
              If KeyAscii >= 97 And KeyAscii <= 122 Then
                    KeyAscii = KeyAscii - 32
              End If
        End Sub