关于用VB写计算器

我自己写的代码...为什么不好用呢~我是刚学VB的~~懂的不是很多~~帮忙看一下代码

Dim num1, num2 As Double
Dim sum As Double
Dim act As Integer

Private Sub Command1_Click(Index As Integer)
Select Case Index
Case 0
If Text1.Text = "" Then
Text1.Text = "0"
End If
Text1.Text = Text1.Text + "0"
Case 1
If Text1.Text = "" Then
Text1.Text = "1"
End If
Text1.Text = Text1.Text + "1"
Case 2
If Text1.Text = "" Then
Text1.Text = "2"
End If
Text1.Text = Text1.Text + "2"
Case 3
If Text1.Text = "" Then
Text1.Text = "3"
End If
Text1.Text = Text1.Text + "3"
Case 4
If Text1.Text = "" Then
Text1.Text = "4"
End If
Text1.Text = Text1.Text + "4"
Case 5
If Text1.Text = "" Then
Text1.Text = "5"
End If<

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