使用VB程序设计使用while语句对输入字符的数字个数和字母个数（如果有字母，统一转化为小写）进行统计的示例代码：

Private Sub CountChars()
Dim strInput As String
Dim intNumCount As Integer
Dim intLetterCount As Integer
Dim intIndex As Integer

'获取输入字符串
strInput = InputBox("请输入字符串:")

'统计数字个数和字母个数
intIndex = 1
While intIndex <= Len(strInput)
'判断当前字符是否为数字
If IsNumeric(Mid(strInput, intIndex, 1)) Then
intNumCount = intNumCount + 1
Else
'转化为小写字母
If Asc(Mid(strInput, intIndex, 1)) >= 65 And Asc(Mid(strInput, intIndex, 1)) <= 90 Then
intLetterCount = intLetterCount + 1
Mid(strInput, intIndex, 1) = Chr(Asc(Mid(strInput, intIndex, 1)) + 32)
End If
End If
intIndex = intIndex + 1
Wend

'输出统计结果
MsgBox "数字个数为：" & intNumCount & vbCrLf & "字母个数为：" & intLetterCount & vbCrLf & "转化后的字符串为：" & strInput
End Sub