图a

从对照表中找出与编号对应的字符完成加密，如下表显示了数字“2018”的加密过程：

小张按照上述原理，设计了一个解密的VB程序，功能如下:单击“解密”按钮Command1,将文本框Text1中的密文(字符数不超过11个)进行解密，并将解密后的明文在文本框Text2中输出。程序运行效果如图a所示。

Const n = 20

Dim a(1 To n) As Integer

Private Sub Command1_Click()

Dim i As Integer

Randomize

For i = 1 To n

  a(i) = Int(Rnd * 1000) + 1

  List1.AddItem Str(a(i))

Next i

End Sub

Private Sub Command2_Click()

Dim i As Integer, max As Integer

Dim min As Integer, sum As Single

max = a(1): min = a(1)

sum = 0

For i = 2 To n

  If {#blank#}1{#/blank#} Then max = a(i)

  If a(i) < min Then min = a(i)

  sum = sum + a(i)

Next i

{#blank#}2{#/blank#}

Text1.Text = Str(max)

Text2.Text = Str(min)

Text3.Text = Str(sum)

End Sub

引起该错误的原因是（  ）