Vb.net 2010 如何创建3个操作数计算器

我正在做一个计算器项目，用2个操作数完成，但很难编码和解决3个操作数的计算。问题是当我这样做的时候，例如，10+10=（答案20）很好，但10+10+10=（也是答案20）。似乎忘记了第一个变量

下面是我在vb2010上的代码，如果我遗漏了什么，请告知。多谢各位

Dim first As Double
Dim second As Double
Dim third As Double
Dim answer As Double
Dim process As String

Private Sub Button15_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button15.Click
    first = Val(TextBox1.Text)
    TextBox1.Text = ""
    formula.Text = first & "x"
    process = "*"
End Sub

Private Sub Button14_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button14.Click
    first = Val(TextBox1.Text)
    TextBox1.Text = ""
    formula.Text = first & "+"
    process = "+"
End Sub

Private Sub Button12_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button12.Click
    first = "0"
    second = "0"
    answer = "0"
    formula.Text = ""
    TextBox1.Text = ""

End Sub

Private Sub Button16_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button16.Click

    If process = "+" Then
        second = Val(TextBox1.Text)
        formula.Text = first & "+" & second & "="
        answer = first + second
        TextBox1.Text = answer
    End If
    If process = "*" Then
        second = Val(TextBox1.Text)
        formula.Text = first & "x" & second & "="
        answer = first * second
        TextBox1.Text = answer
    End If
    If process = "/" Then
        second = Val(TextBox1.Text)
        formula.Text = first & "÷" & second & "="
        answer = first / second
        TextBox1.Text = answer
    End If

    If process = "-" Then
        second = Val(TextBox1.Text)
        formula.Text = first & "-" & second & "="
        answer = first - second
        TextBox1.Text = ""
    End If
   
End Sub


Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
    first = Val(TextBox1.Text)
    TextBox1.Text = ""
    formula.Text = first & "-"
    process = "-"
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    first = Val(TextBox1.Text)
    TextBox1.Text = ""
    formula.Text = first & "÷"
    process = "/"
End Sub

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感谢您检查此查询的人。我通过重新编写代码找到了解决方案，并将其发布在youtube上，以帮助其他可能需要它的人，[link]（）更新了youtube[link]（）