当输入的运算符不是加、减、乘、除四种运算符时，则输出“运算符不正确”；当进行除法运算时，如果除数为0，提示输出“除数不能为零”。相应的Visual Basic程序如下，在①和②划线处，填入合适的语句或表达式，把程序补充完整。

Private Sub Command1_Click（）

    Dim a As Single, b As Single, ch As String

    a = Val(Text1.Text)

    b = Val(Text2.Text)

             ①      

    If ch = "+" Then

        Text4.Text = Str(a + b)

    ElseIf ch = "*" Then

        Text4.Text = Str(a * b)

    ElseIf ch = "-" Then

        Text4.Text = Str(a - b)

    ElseIf ch = "/" Then

        If  ②  Then Text4.Text = Str(a / b) Else Text4.Text = "除数不能是零"

    Else

                 ③     

    End If

End Sub

Dim a(1 To 10) As Integer, b(5 To 10) As Integer

a(1) = 71: a(2) = 73: a(3) = 90: a(4) = 79: a(5)  = 76

a(6) = 88: a(7) = 91: a(8) = 84: a(9) = 100: a(10) = 80

For i = 10 To 1 Step -1

  b((a(i) - 1) \ 10) = b((a(i) - 1) \ 10) + 1

Next i

该程序段运行后，数组元素b(7)的值是（  ）

实现上述功能的VB程序如下，请在划线处填入合适的代码。

Private Sub Command1_Click()

Dim s1 As String

Dim s2 As String

Dim s3 As String

Dim l1 As Integer

Dim l2 As Integer

Dim l3 As Integer

Dim a(1 To 100) As Integer

Dim b(1 To 100) As Integer

Dim c(1 To 100) As Integer

Dim t As Integer

s1 = Text1.Text

s2 = Text2.Text

l1 = Len(s1)

l2 = Len(s2)

For i = l1 To 1 Step -1

 a(i) ={#blank#}1{#/blank#}

Next

For i = l2 To 1 Step -1

 b(i) =Val(Mid(s2, l2 - i + 1, 1))

Next

If l1 > l2 Then l3 = l1 Else l3 = l2

t = 0

For i = 1 To l3

  c(i) = a(i) + b(i) + t

  t = c(i) \ 10

  c(i) ={#blank#}2{#/blank#}

Next

For i = 1 To l3

  s3 = Str(c(i)) + s3

Next

If{#blank#}3{#/blank#}Then s3 = “1” + s3

Text3.Text = s3

End Sub