请问这个vb语句中的searchn=-1是什么含义

Private Sub Form_click()
Dim a(1 To 6) As Integer, i As Integer, key As Integer, searchn As Integer
For i = 1 To 6
a(i) = Val(InputBox("输入第" + Str(i) + "个数"))
Next i
searchn = -1
key = InputBox("输入要查找的数据")
For i = LBound(a) To UBound(a)
If key = a(i) Then
searchn = i
Exit For
End If
Next i
If searchn = -1 Then
Print "数据未找到"
Else
Print "找到的数据为:"; a(searchn)
End If
End Sub

赋初值，当以下标跟踪方式搜索到数组a()中所查找的数据时，便被赋值为当前下标值。
说白了，赋值-1只是为了验证有没有搜索到数据，只要不与a()数组的下标冲突赋值什么数都无所谓。这个程序完全可以将该语句省略，因为0和1 to 6不冲突。
Private Sub Form_click()
Dim a(1 To 6) As Integer, i As Integer, key As Integer, searchn As Integer
For i = 1 To 6
a(i) = Val(InputBox("输入第" + Str(i) + "个数"))
Next i
key = InputBox("输入要查找的数据")
For i = LBound(a) To UBound(a)
If key = a(i) Then
searchn = i
Exit For
End If
Next i
If searchn Then
Print "数据未找到"
Else
Print "找到的数据为:"; a(searchn)
End If
End Sub

额