Evaluate Arithmetic Expressions using Polish Notations in VB.NET

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Introduction

This sample application illustrates how to solve arithmetic expressions using Polish notation (logic for solving arithmetic expressions).

In this source code, I have used a stack and queue and some of their important methods like pop, push etc.

Using the Code

You can use this code in your application. You can create a class, and call the function Evaluate(str) to evaluate the expression. Create a class and copy the following code into the class:

Imports System.Math
Public Class EvaluateArithmeticExp
    '
    'Declaration
    '

    Dim k As Integer = 0
    Dim Stack1 As New Stack() ' Declaring Stacks
    Dim Postfix As New Queue()
    Dim Ch, NextChar As String
    Dim StrInfix As String ' Input String
    Dim Prece As Integer ' For Precendence of Operator
    Dim Infix As String()
    Dim i As Integer
    Dim j As Integer

    Private Function Space(ByVal C As Char) As Boolean
        If C = CType(ChrW(System.Windows.Forms.Keys.Space), Char) _
               Or C = CType(CChar(CStr(System.Windows.Forms.Keys.Tab)), Char) Then
            Return True
        Else
            Return False
        End If
    End Function

    Private Function Precedence(ByVal C As String) As Integer
        If C = "(" Then
            Return 0
        ElseIf C = "+" Or C = "-" Then
            Return 1
        ElseIf C = "*" Or C = "/" Or C = "%" Then
            Return 2
        ElseIf C = "^" Then
            Return 3
        End If
    End Function

    '
    'Function For Convert Input String Into An Array
    '
    Private Sub CreateInfix(ByVal str As String)
        j = 0
        Dim separetor(7) As Char
        Dim c As Integer = 0
        separetor(c) = "+" : c += 1
        separetor(c) = "-" : c += 1
        separetor(c) = "*" : c += 1
        separetor(c) = "/" : c += 1
        separetor(c) = "%" : c += 1
        separetor(c) = "(" : c += 1
        separetor(c) = ")" : c += 1
        separetor(c) = "^"

        Dim posF, posL As Integer
        posF = 0
        posL = 0
        ReDim Infix(str.Length + 5)

        For i = 0 To str.Length - 1
            posL = str.IndexOfAny(separetor, posF)
            If posL > str.Length Or posL < 0 Then
                Exit For
            Else
                Infix(j) = Trim(Mid(str, posF + 1, posL - posF)) : j += 1
                posF = posL + 1
                Infix(j) = Mid(str, posL + 1, 1) : j += 1
            End If
        Next
        Infix(j) = Trim(Mid(str, posF + 1, str.Length))
    End Sub

    '
    'Function to Evaluate Postfix Expression 
    '
    Private Sub Evaluate_Postfix()
        Dim Operands1, Operands2, Result As Long
        Dim Operand_Operators As String
        Try
            For i = 1 To Postfix.Count
                Operand_Operators = Postfix.Dequeue
                If IsNumeric(Operand_Operators) Then
                    Stack1.Push(Operand_Operators)
                Else
                    Operands1 = Stack1.Pop
                    Operands2 = Stack1.Pop
                    If Operand_Operators = "+" Then
                        Result = Operands2 + Operands1
                    ElseIf Operand_Operators = "-" Then
                        Result = Operands2 - Operands1
                    ElseIf Operand_Operators = "*" Then
                        Result = Operands2 * Operands1
                    ElseIf Operand_Operators = "/" Then
                        Result = Operands2 / Operands1
                    ElseIf Operand_Operators = "%" Then
                        DivRem(Operands2, Operands1, Result)
                    ElseIf Operand_Operators = "^" Then
                        Result = Pow(Operands2, Operands1)
                    End If
                    Stack1.Push(Result)
                End If
            Next
        Catch ex As Exception
            MsgBox("Error :" & vbCrLf & vbCrLf & _
                   "Input String Is Not Currect." & vbCrLf & ex.Message)
        End Try
    End Sub

    Public Function Evaluate(ByVal Str As String) As Long
        Postfix.Clear()
        StrInfix = ""
        Stack1.Clear()
        StrInfix = Str
        Call CreateInfix(StrInfix)
        '
        'Convert Infix Expression To Postfix Expression (Login Polish Notation)
        '
        Try
            For i = 1 To Infix.Length
                Ch = Infix(i - 1)
                If Not Space(Ch) Or Not IsDBNull(Ch) Then
                    If System.Char.IsDigit(Ch) Then
                        Postfix.Enqueue(Ch)
                    ElseIf Ch = "(" Then
                        Stack1.Push(Ch)
                    ElseIf Ch = ")" Then
                        Do
                            If Not Stack1.Count = 0 Then
                                NextChar = Stack1.Pop
                                If NextChar = "(" Then
                                    NextChar = ""
                                    Exit Do
                                Else
                                    Postfix.Enqueue(NextChar)
                                End If
                                Else
                                Exit Do
                            End If
                        Loop
                    ElseIf Ch = "+" Or Ch = "-" Or _
                                Ch = "*" Or Ch = "/" Or _
                                Ch = "%" Or Ch = "^" Then
                        Prece = Precedence(Ch)
                        Do
                            If Not Stack1.Count = 0 Then
                                If Prece <= Precedence(Stack1.Peek) Then
                                    Postfix.Enqueue(Stack1.Pop)
                                Else
                                    Exit Do
                                End If
                            Else
                                Exit Do
                            End If
                        Loop
                        Stack1.Push(Ch)
                    End If
                End If
            Next

            For i = 0 To Stack1.Count - 1
                Postfix.Enqueue(Stack1.Pop)
            Next

            Call Evaluate_Postfix()
        Catch ex As Exception
            MsgBox("Error :" & vbCrLf & vbCrLf & _
                   "Input String Is Not Currect." & _
                   vbCrLf & ex.Message)
            Return 0
            Exit Function
        End Try
        Return Stack1.Pop
    End Function
End Class