VB.NET 计算包含变量的字符串

Question

我喜欢用不同的公式填充我的数据库。

当我在数据库中有一个公式时，例如"(2+4)*5"我得到的结果40：

update DB.dbo.INFOGROUP SET formula = '(2+4)*5' where INFOGROUP = 'S42'

当我在数据库中有一个公式时，例如"(x+4)*5"我得到的结果20.即使我将x的值设置为10，也会忽略x值：

update DB.dbo.INFOGROUP SET formula = '(x+4)*5' where INFOGROUP = 'S42'

Private Sub BtnCalculate_Click(sender As Object, e As EventArgs) Handles BtnCalculate.Click
Dim SC As New MSScriptControl.ScriptControl
Dim x As Double = 10
SQL.AddParam("@infogroup", "S42")
SQL.ExecQuery($"SELECT formula FROM DB.dbo.INFOGROEP where infogroep=@infogroep")
Dim Formula As String = <string_from_db>
'SET LANGUAGE TO VBSCRIPT
SC.Language = "VBSCRIPT"
'ATTEMPT MATH
Try
Dim Result As Double = Convert.ToDouble(SC.Eval(Formula))
'SHOW THAT IT WAS VALID
MessageBox.Show("Math success, " & Formula & " equals " & Result.ToString)
Catch ex As Exception
'SHOW THAT IT WAS INVALID
MessageBox.Show("Not a valid math formula for a double.")
End Try
End Sub

这是否可能，或者我是否需要第三方脚本？

顺便说一句：在Visual Foxpro中有一个类似于EVAL(db_string)的功能。

Answer 1

脚本引擎不了解方法中的变量。 如果要计算包含变量的公式，则需要告诉它该变量具有什么值：

SC.Language = "VBSCRIPT"
sc.AddCode "Private Const x = 10"
Dim Result As Double = Convert.ToDouble(SC.Eval(Formula))