用VB6做一个简单的加法运算，这个VB程序代码下划线部分应该写什么

Private Sub Command l_ClickO
Dim key As String
Dim a As Integer, s As Integer, ans As Integer, ch As String
key = Textl .Text
i=l
Do While i<=Len(key)
ch=Mid(key, i ,1)
If ch >= "0" And ch <= "9，， Then
                                 
Else
Exit Do
End If
Loop
a=                  
b=Val(Mid(key，i+1 ,________)
ans=a+b
Labell.Caption=”算式计算结果为” + str (ans)
End Sub

[此贴子已经被作者于2019-6-7 19:59编辑过]