我想做一个我输入数字 自己能加减乘除得出结果的软件得怎么做?有没有会的简单么?

dima1$, a2$, a3$
Private Sub Command1_Click(Index As Integer)
a1 = a1 + Command1(Index).Caption
Text1.Text = a1
End SubPrivate Sub Command2_Click()
Select Case a3
Case "+"
a1 = Val(a2) + Val(a1)
Case "-"
a1 = Val(a2) - Val(a1)
Case "*"
a1 = Val(a2) * Val(a1)
Case "/"
a1 = Val(a2) / Val(a1)
End Select
Text1.Text = a1
End SubPrivate Sub Command3_Click(Index As Integer)
a3 = Command3(Index).Caption
Text1.Text = a3
a2 = a1
a1 = ""
End SubPrivate Sub Command4_Click()
If a1 "" Then
If InStr(a1, "-") = 0 Then
a1 = "-" + a1
Text1.Text = a1
End If
End If
End SubPrivate Sub Command5_Click()
If a1 "" Then
If InStr(a1, ".") = 0 Then
a1 = a1 + "."
Text1.Text = a1
End If
End If
End SubPrivate Sub Command6_Click()
If a1 "" Then
a1 = Left(a1, Len(a1) - 1)
Text1.Text = a1
End If
End SubPrivate Sub Command7_Click()
a1 = ""
Text1.Text = a1
End Sub
再问： 这是什么呀？