填空题 下面程序的功能是统计字符串中“i”的个数，请填空。 Sub COU( ) Dim n As Integer a$ = "Beijing University of Technology" n = Len(a$ ) For i = 1 To n b$ =Mid$(a$,i, 1) If{{U}} 【11】 {{/U}}Then x=x + 1 Next Print "x ="; x End Sub