等差等比計算機（有缺陷版）

Public Class Form1

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
If ListBox1.SelectedItem = "等差數列" Then
If ListBox2.SelectedItem = "求合（請至少輸入首項公差（比）和項數）" Then
q.Text = n.Text * (2 * a1.Text + (n.Text - 1) * r.Text) / 2
End If
If ListBox2.SelectedItem = "求第N的質（請至少輸入首項公差第N項輸入至項數）" Then
q.Text = a1.Text + (n.Text - 1) * r.Text
End If
If ListBox2.SelectedItem = "求此數為第n項（同上 此數輸入至末項中）" Then
q.Text = -((-an.Text + a1.Text - r.Text) / r.Text)
End If
If ListBox2.SelectedItem = "求公差（公比）（請至少輸入首項第二項）" Then
q.Text = a2.Text - a1.Text
End If
If ListBox2.SelectedItem = "求公差（公比）（請至少輸入首項末項項數）" Then
q.Text = (an.Text - a1.Text) / (n.Text - 1)
End If

End If
If ListBox1.SelectedItem = "等比數列" Then
If ListBox2.SelectedItem = "求合（請至少輸入首項公差（比）和項數）" Then
q.Text = (a1.Text * (1 - r.Text ^ n.Text)) / (1 - r.Text)
End If
If ListBox2.SelectedItem = "求第N的質（請至少輸入首項公差第N項輸入至項數）" Then
q.Text = a1.Text * r.Text ^ (n.Text - 1)
End If
If ListBox2.SelectedItem = "求此數為第n項（同上 此數輸入至末項中）" Then
MsgBox("很抱歉我公式倒不出來所以不能用")
End If
If ListBox2.SelectedItem = "求公差（公比）（請至少輸入首項第二項）" Then
q.Text = a2.Text / a1.Text
End If
If ListBox2.SelectedItem = "求公差（公比）（請至少輸入首項末項項數）" Then
MsgBox("很抱歉我公式倒不出來所以不能用")
End If



End If
End Sub
End Class