以下程序的功能是,从字符串s1的头尾至中间依次各取一个字符,组成一个新字符串s并进行显示,其中假设s1中含有的字符个数为偶数。请补充完整程序中的空白处。 Private Sub Form_Click() Dim s1 As String, s As String Dim L As Integer, n As Integer s1 = "ABCDEFGHIJKLMNOP" L = Len(s1) n = 1 Do While n <= Int(L/2) s = s + Mid( ) + Mid( ) n = n + 1 Loop Print s End Sub