单项选择题

有如下程序：
Private Sub Form_Click( )
Dim n As Integer, a As String
Dim L As Integer, C As Integer
n = InputBox("请输入一个整数")
For i = 1 To n
a = InputBox("请输入一个字符串")
L = Len(A)
C = 0
For j = 1 To L
If Mid(a, j, 1) = "D" Then
C = C+1
End If
Next j
Print a; C
Next i
End Sub
以上程序的功能是______。