VB "Conversion from string "s“键入 'Boolean' 无效。”

Question

如果重要的话，我正在使用 Visual Studio Express 2012 和 Windows 7 Professional。

我有一个抛出此异常的简单 VB 程序：

An unhandled exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll

Conversion from string "s" to type 'Boolean' is not valid.

这是代码的麻烦部分：

If stroperation = "S" Or "s" Then

我做错了什么？

整个VB程序：

Public Class MainForm
Public stroperation, strnumber1, strnumber2, strresult As String
Public decnumber1, decnumber2, decresult As Decimal
Public operation
Private Sub calculateButton_Click(sender As Object, e As EventArgs) Handles calculateButton.Click
    operation = operationTextBox.Text
    stroperation = CStr(operation)
    strnumber1 = number1TextBox.Text
    decnumber1 = CDec(strnumber1)
    strnumber2 = number2TextBox.Text
    decnumber2 = CDec(strnumber2)
    If stroperation = "S" Or "s" Then
        decresult = decnumber1 - decnumber2
        resultLabel.Text = "Difference: " & strresult
    ElseIf stroperation = "A" Or "a" Then
        decresult = decnumber1 + decnumber2
        resultLabel.Text = "Sum: " & strresult
    Else
        MsgBox("Enter A, a, S, or S.")
    End If
End Sub
End Class

Answer 1

您需要将其更改为If stroperation = "S" Or stroperation = "s" Then

或者更好的是，您可以这样做：

If stroperation.Equals("S", StringComparison.CurrentCultureIgnoreCase) Then

VB "Conversion from string "s“键入 'Boolean' 无效。”

VB "Conversion from string "s" to type 'Boolean' is not valid."

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