以下是我在网上找的小程序（它结果输出是13）。
请在每句添加注释。它的运行原理。
Private x, y As Integer
Private Sub Form_Click()
Dim a, b As Integer
a = 5
x = 2
y = 3
b= z(a)
Print "第" & 5 & "项是" & b
End Sub
Function z(a As Integer)
If a = 1 Then
z = x
ElseIf a = 2 Then
z= y
Else
z = z(a - 2) + myfunc(a - 1)
End If
End Function
z = z(a - 2) + myfunc(a - 1)这条代码应改为z = z(a - 2) +z(a - 1)
