【加试题】小王模拟超市收银机扫描商品条形码后计算总价的过程制作了一个VB程序。功能如下：在文本框Text1中输入商品条形码，按回车键后会将已经输入的条形码显示在列表框List1中，同时将商品明细显示在列表框List2中。点击按钮“计算商品总价”后，会将所有商品的总价显示在文本框Text2中。程序界面如图所示：

实现上述功能的部分VB程序如下，请在三个划线处填入合适代码。
'定义全局数组变量
Dim a(1 To 10) As Long
Dim b(1 To 10) As String
'自动加载条形码信息以及对应的商品信息
Private Sub Form_Load()
Dim i As Integer
a(1) = 503741
For i =" 2" To 10
a(i) =" a(i" - 1) + 1
Next i
b(1) = "可乐 5.00"
b(2) = "薯片 7.50"
b(3) = "牛奶 5.60"
b(4) = "橙汁 7.50"
b(5) = "面包 4.00"
b(6) = "蜂蜜 28.00"
b(7) = "蛋糕 12.00"
b(8) = "绿箭 3.50"
b(9) = "饼干 6.00"
b(10) = "雪碧 5.00"
End Sub
'输入条形码，查找条形码，并显示条形码及其对应的商品信息
Private Sub Text1_KeyPress(KeyAscii As Integer)
Dim txm As Long:
Dim i As Integer:
Dim j As Integer
txm = Val(Text1.Text)
If KeyAscii =" 13" Then
If txm >=" 503741" And txm <=" 503750" Then
List1.AddItem txm
Text1.Text = ""
i =" 1:" j = 10
Do While i <= j
    ①
If txm =" a(m)" Then
List2.AddItem b(m)
Exit Do
ElseIf txm > a(m) Then
i =" m" + 1
Else
   ②   
End If
Loop
Else
MsgBox "条形码输入错误，无此商品"
Text1.Text = ""
End If
End If
End Sub
'计算所购商品的总额
Private Sub Command1_Click()
Dim i As Integer, mx As String, jg As String, sum As Single
For i =" 0" To 9
If List2.List(i) <> "" Then
mx = List2.List(i)
sum =" sum" + Mid(mx, 4)
End If
Next i
Text2.Text = ③    
End Sub