VB求三角函数

我有一个问题，关于求三角函数，需要用户输入角度 弧度，然后选择SIN COS TAN，用LABEL显示界面是这样的

♂Amour♂ 12:47:50
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Dim a1 As Integer

Private Sub Command1_Click()
a1 = Val(Text1.Text)
If Combo1.Text = "求Sin" And Combo2.Text = "弧度" Then
Label1.Caption = Sin(a1 * 3.14 / 180)
If Combo1.Text = "求Cos" And Combo2.Text = "弧度" Then
Label1.Caption = Cos(a1 * 3.14 / 180)
If Combo1.Text = "求Tan" And Combo2.Text = "弧度" Then
Label1.Caption = Tan(a1 * 3.14 / 180)
If Combo1.Text = "求Sin" And Combo2.Text = "角度" Then
Label1.Caption = Sin(a1)
If Combo1.Text = "求Cos" And Combo2.Text = "角度" Then
Label1.Caption = Cos(a1)
If Combo1.Text = "求Tan" And Combo2.Text = "角度" Then
Label1.Caption = Tan(a1)
End If
End If
End If
End If
End If
End If

End Sub

Private Sub Form_Load()
Combo

If Combo1.Text = "求Sin" And Combo2.Text = "弧度" Then
Label1.Caption = Sin(a1 * 3.14 / 180)
If Combo1.Text = "求Cos" And Combo2.Text = "弧度" Then
Label1.Caption = Cos(a1 * 3.14 / 180)
If Combo1.Text = "求Tan" And Combo2.Text = "弧度" Then
Label1.Caption = Tan(a1 * 3.14 / 180)
If Combo1.Text = "求Sin" And Combo2.Text = "角度" Then
Label1.Caption = Sin(a1)
If Combo1.Text = "求Cos" And Combo2.Text = "角度" Then
Label1.Caption = Cos(a1)
If Combo1.Text = "求Tan" And Combo2.Text = "角度" Then
Label1.Caption = Tan(a1)
End If
End If
End If
End If
End If
End If
逻辑不对,改成下面这样
If Combo1.Text = "求Sin" And Combo2.Text = "弧度" Then
Label1.Caption = Sin(a1 * 3.14 / 180)
End If
If Combo1.Text = "求Cos" And Combo2.Text = "弧度" Then