VB.NET Math Parser Example

This example is very similar to Visual Basic 6 Math Parser Example. The main difference is the attachment of event handlers in the code. Events are used to invoke user defined functions. Unlike Visual Basic 6, VB.NET requires us to use COM Interoperability facilities to register our event handler functions.

Option Strict Off
Option Explicit On

'imports BCPARSERLib

Friend Class Form1
Inherits System.Windows.Forms.Form
Dim Parser As BCPARSERLib.Parser
Private Sub Command1_Click(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles Command1.Click

On Error GoTo HandleError
'create our parser object:
Parser = New BCPARSERLib.Parser

'In VB.NET, we need to register event handler in a different way that .NET COM Interoperability requires:
AddHandler Parser.OnExecOneParamFunc, New BCPARSERLib._IParserEvents_OnExecOneParamFuncEventHandler(AddressOf Parser_OnExecOneParamFunc)
AddHandler Parser.OnExecTwoParamFunc, New BCPARSERLib._IParserEvents_OnExecTwoParamFuncEventHandler(AddressOf Parser_OnExecTwoParamFunc)
AddHandler Parser.OnExec3ParamFunc, New BCPARSERLib._IParserEvents_OnExec3ParamFuncEventHandler(AddressOf Parser_OnExec3ParamFunc)
AddHandler Parser.OnExecNParamFunc, New BCPARSERLib._IParserEvents_OnExecNParamFuncEventHandler(AddressOf Parser_OnExecNParamFunc)

'create a custom function that takes two parameters:
Parser.CreateOneParamFunc("one")
Parser.CreateTwoParamFunc("two")
Parser.Create3ParamFunc("three")
Parser.CreateNParamFunc("myavg")

Parser.Expression = Text1.Text

'MsgBox "Expression is set fine. Expression is: " + Parser.Expression, vbOKOnly

Parser.X = 7 'we set X, Y variables' values this way.
Parser.Variable("X") = 8 'we set any variable's value this way.
Parser.Variable("myvar") = 10 'this will also create a variable if it does not exist.

If Parser.IsVariable("x") Then 'variable case does not matter.
MsgBox("Yes, X is a variable.", MsgBoxStyle.OKOnly)
End If
If Parser.IsVariableUsed("X") Then 'we can detect if it is used in the current expression.
MsgBox("Yes, X is used in the expression.", MsgBoxStyle.OKOnly)
End If
'Parser.IsVariableUsed("Y") would return false because Y is not used for example.

'display variable value
LabelXVal.Text = CStr(Parser.X)

'Don't Allow Division by Zero:
Parser.StrictFloatingPoint = True

'get the result:
Label1.Text = CStr(Parser.Value)

'For i = 0 To 100000000
' Parser.Evaluate
'Next

Exit Sub

HandleError:
MsgBox(Err.Description, MsgBoxStyle.OKOnly)
MsgBox("Forgot to declare variable? " & Parser.GetInvalidPortionOfExpression(), MsgBoxStyle.OKOnly)

End Sub
Private Sub Form1_Load(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles MyBase.Load
'Text1.Text = "IF(X, SIN(X+1), Y)"
Text1.Text = "one(X+1) + two(50, 100) + three(100,200,300)"
End Sub

Private Function Parser_OnExecNParamFunc(ByVal FuncName As String, ByRef params As System.Array) As Double
Dim i As Integer
Dim Sum As Double
If FuncName = "MYAVG" Then 'compute avarage
Sum = 0
For i = LBound(params) To UBound(params)
Sum = Sum + params(i)
Next
Parser_OnExecNParamFunc = 1 'Sum / (UBound(params) - LBound(params))
Else
Parser_OnExecNParamFunc = 0
End If
End Function

Private Function Parser_OnExecOneParamFunc(ByVal FuncName As String, ByVal param1 As Double) As Double
Dim RetVal As Double
MsgBox("Calculating func value for " & FuncName, MsgBoxStyle.OKOnly)
If (FuncName = "ONE") Then
MsgBox("Param1 is " & Str(param1), MsgBoxStyle.OKOnly)
RetVal = param1 + 1
MsgBox("RetVal is " & Str(RetVal), MsgBoxStyle.OkOnly)
End If
Parser_OnExecOneParamFunc = RetVal
End Function

Private Function Parser_OnExecTwoParamFunc(ByVal FuncName As String, ByVal param1 As Double, ByVal param2 As Double) As Double
Dim RetVal As Double
MsgBox("Calculating func value for " & FuncName, MsgBoxStyle.OKOnly)
If (FuncName = "TWO") Then 'note that function name is upper case "MYCUSTOMFUNC"
MsgBox("Param1 is " & Str(param1), MsgBoxStyle.OKOnly)
MsgBox("Param2 is " & Str(param2), MsgBoxStyle.OKOnly)
RetVal = param1 + param2
MsgBox("RetVal is " & Str(RetVal), MsgBoxStyle.OkOnly)
End If
Parser_OnExecTwoParamFunc = RetVal
End Function

Private Function Parser_OnExec3ParamFunc(ByVal FuncName As String, ByVal param1 As Double, ByVal param2 As Double, ByVal param3 As Double) As Double
Dim RetVal As Double
MsgBox("Calculating func value for " & FuncName, MsgBoxStyle.OKOnly)
If (FuncName = "THREE") Then
MsgBox("Param1 is " & Str(param1), MsgBoxStyle.OKOnly)
MsgBox("Param2 is " & Str(param2), MsgBoxStyle.OKOnly)
MsgBox("Param3 is " & Str(param3), MsgBoxStyle.OKOnly)
RetVal = param1 + param2 + param3
MsgBox("RetVal is " & Str(RetVal), MsgBoxStyle.OkOnly)
End If
Parser_OnExec3ParamFunc = RetVal
End Function
End Class

Here is another example of handling parser events in Visual Basic 2008:
Notice the Handles Parser.OnExecOneParamFunc

Public Class Form1
Dim WithEvents Parser As BCPARSERLib.Parser

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Parser = New BCPARSERLib.Parser
Parser.CreateOneParamFunc("test") 'It will be uppercase TEST
Parser.Expression = TextBox1.Text
Parser.X = 5
Parser.StrictFloatingPoint = False
Parser.OptimizationOn = True
Label1.Text = Str(Parser.Value)
Parser = Nothing
End Sub

Private Function Parser_OnExecOneParamFunc(ByVal FuncName As String, ByVal param1 As Double) As Double Handles Parser.OnExecOneParamFunc
Dim retval As Double
retval = 0
If (FuncName = "TEST") Then
retval = param1 * 2
End If
Parser_OnExecOneParamFunc = retval
End Function
End Class

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