Vb.net 错误1局部变量'；美元'；是否已在当前块中声明？是否在我的程序中声明？

我已经多次修改代码，试图编写一个货币转换程序，将美元兑换成加拿大或墨西哥的汇率告知如下，我不断得到错误信息：

Error 1 Local variable 'USD' is already declared in the current block. C:\Users\dgrossi0914\Documents\Visual Studio 2013\Projects\Program3\Program3\Program3\Form1.vb 9 13 Program3

My code is as follows:

Public Class Form1
    Private Sub US_Dollar_TextChanged(sender As Object, e As EventArgs) Handles US_Dollar.TextChanged
        Const Canadian_Dollar As Decimal = 1.13
        Const Mexican_Peso As Decimal = 11.03
        Dim US_Dollar As String = 1.0
        Dim USD As Single 'makes USD member of Single
        Decimal.TryParse(US_Dollar, USD)
        ConRate.Text = Val(USD.Text) * Val(Canadian_Dollar) 'helps with constant
        Dim USD As Single 'makes USD member of Single
        US_Dollar = Convert.ToString(USD)
        ConRate = Val(USD.Text) * Val(Mexican_Peso) 'helps with constant
        US_Dollar = Format(1, "$0.00")
    End Sub

    Private Sub ConRate_TextChanged(sender As Object, e As EventArgs) Handles ConRate.TextChanged

    End Sub

    Private Sub Canadian_Click(sender As Object, e As EventArgs) Handles Canadian_Dollar.Click
        ConRate.Text = US_Dollar.Text & " U.S._Dollar(s) " & " equal " & Val(US_Dollar.Text) * Val(Canadian_Dollar.Text) & " Canadian Dollars"
    End Sub

    Private Sub Mexican_Click(sender As Object, e As EventArgs) Handles Mexican_Peso.Click
        ConRate.Text = US_Dollar.Text & " U.S._Dollar(s) " & " equal " & Val(US_Dollar.Text) * Val(Mexican_Peso.Text) & " Mexican Pesos"
    End Sub

    Private Sub ClrButton_Click(sender As Object, e As EventArgs) Handles ClrButton.Click
        US_Dollar.Text = ""
        ConRate.Text = ""
    End Sub

    Private Sub XitButton_Click(sender As Object, e As EventArgs) Handles XitButton.Click
        Me.Close()
    End Sub

End Class

我试过这本书，它对我有所帮助，我看了所有的教程，我试着在互联网上寻找例子

然而，这本书确实对解决这个问题有很大帮助，没有像这样的辅导，我付费加入了learnvideostudio.net，但它确实让我提出了一个问题

这么说来，你有没有比他们建议的更好的建议来解决这个问题，因为我想我的导师正试图告诉我使用Dim USD作为单数两次。一次在解析之前，另一次在转换tco字符串之前，这给了我上面提到的错误。然而，如果我将第二个Dim USD作为Single删除，那么我会得到错误USD而不是Single的成员

---

我该怎么办？

错误消息几乎是自我描述的。有一个变量声明了不止一次，事实上它是正确的。此行在

US\u Dollar\u TextChanged

方法中复制两次：

Dim USD As Single 'makes USD member of Single

---

只要删除最后一个，它就会工作。我不理解如果删除它会出现什么错误，但首先要删除第二行，然后再阅读您收到的确切消息。

似乎很明显。你在班上有两次

Dim USD

。