将字符串转换为运算符

Question

在我的 VB.Net 4.5 WPF 应用程序中，我有 3 个文本框供用户输入以下内容：

1. txtFirstNumber
2. txt运算符
3. txtSecondNumber

问题：我发现我无法将运算符字符串转换为实际的数学运算符，因为运算符没有数据类型。

我无法使用 + 或 & 或 val 或 eval 来计算：txtFirstNumber txtOperator txtSecondNumber

例如：如果用户输入 12 作为 firstNumber，+ 作为运算符，5 作为 secondNumber，那么我想自动计算 12 + 5 并将答案放在名为 CalculateAnswer 的标签中。

如果用户输入不同的内容，我希望仍然进行计算。即使他们输入双精度数作为其中一个数字。

所以我需要帮助！这是我的代码：

    Dim CalcAnswer As Double
    Try
        Dim first As Double = CDbl(txtFirstNumber.Text)
        Dim op As String = txtOperator.Text
        Dim second As Double = CDbl(txtSecondNumber.Text)
        CalcAnswer = Eval(first & op & second)
        CalculateAnswer.Content = CStr(CalcAnswer)
    Catch CalcError As Exception
        MsgBox(CalcError.Message)
    End Try

提前致谢！

Answer 1

我会这样做：

Try
    Dim first As Decimal = Decimal.Parse(txtFirstNumber.Text)
    Dim second As Decimal = Decimal.Parse(txtSecondNumber.Text)
    CalculateAnswer.Content = Eval(first, second, txtOperator.Text).ToString()
Catch CalcError As Exception
    MsgBox(CalcError.Message)
End Try

'...

Function Add(ByVal a As Decimal, ByVal b As Decimal) As Decimal
   Return a + b
End Function

Function Subtract(ByVal a As Decimal, ByVal b As Decimal) As Decimal
   Return a - b
End Function

Function Multiply(ByVal a As Decimal, ByVal b As Decimal) As Decimal
   Return a * b
End Function

Function Divide(ByVal a As Decimal, ByVal b As Decimal) As Decimal
   Return a / b
End Function

Function Eval(ByVal a As Decimal, ByVal b As Decimal, ByVal Operator As String) As Decimal
   Operator = Operator.Trim()
   Select Operator
      Case "+"
        Return Add(a, b)
      Case "-"
        Return Subtract(a, b)
      Case "*","x"
        Return Multiply(a, b)
      Case "/"
         Return Divide(a, b)
      Case Else 
          Throw New InvalidArgumentException("Did not recognize operator: " & Operator)
   End Select
End Function