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$)
For i = 1 To n
b$ = 【15】
If b$ ="i" Then x=x+1
Next
Print" x="; x
End Sub

【参考答案】

Mid$(a$,i,1) b$=“i”