填空题

下面这个Sub过程的功能是统计字符串中“a”的个数，请在空白处填上合适的代码完成程序。 Private Sub numCount() Dim hum As Integer s＄ = "software And hardware" num = Len(s$) For i = 1 To hum b$=______ If b$ = "a" Then x = x+1 Next i Print "x="; x End Sub