vb编程语言中怎么通过获取一个变量的值去算它在数组中下标的integer值？

vb编程语言中怎么通过获取一个变量的值去算它在数组中下标的integer值？获取下标integer值的代码怎么思路？

http://www.myexception.cn/program/1716121.html

    Dim a()     As Long
    Dim v       As Long
    Dim i       As Long

    ReDim a(1 To 3)
    a(1) = 100
    a(2) = 300
    a(3) = 200
    v = 300

    For i = 1 To 3
        If a(i) = v Then
            Debug.Print "找到下标：" & i
            Exit For
        End If
    Next