Simple reverse polish notation calculator written in VB.NET (no division support!)

rpncal.vb

Imports System

Module Program
    Sub PrintHelp()
        Console.WriteLine("rpncalc - version 0.1 - 2022")
        Console.WriteLine("To use: type integer or operator")
        Console.WriteLine("")
        Console.WriteLine("Operators:")
        Console.WriteLine("    +        Adds all values on the stack together.")
        Console.WriteLine("    -        Substracts all values on the stack from each other.")
        Console.WriteLine("    *        Multiplies all values on the stack together.")
        Console.WriteLine("    i        Print all stack values to the terminal.")
        Console.WriteLine("    q        Quit the REPL.")
    End Sub

    Sub Main(args As String())
        Dim running As Boolean = True
        Dim stack As New List(Of Integer)

        If args.Length <> 0 Then
            PrintHelp()
            Return
        End If

        While running
            Console.Write("> ")

            Dim currentInput As String = Console.ReadLine()
            currentInput = currentInput.Trim()

            Select Case currentInput
                Case "+"
                    Dim result As Integer = 0

                    For Each item In stack
                        result += item
                    Next

                    stack.Clear()
                    stack.Add(result)
                    Console.WriteLine(String.Format("Result: {0}", result))
                Case "-"
                    Dim result As Integer = 0

                    For Each item In stack
                        result -= item
                    Next

                    stack.Clear()
                    stack.Add(result)
                    Console.WriteLine(String.Format("Result: {0}", result))
                Case "*"
                    Dim result As Integer = 1

                    For Each item In stack
                        result *= item
                    Next

                    stack.Clear()
                    stack.Add(result)
                    Console.WriteLine(String.Format("Result: {0}", result))
                Case "i"
                    For Each item In stack
                        Console.WriteLine(item)
                    Next
                Case "q"
                    running = False
                    Continue While
                Case Else
                    Try
                        Dim parsed As Integer = Integer.Parse(currentInput)

                        stack.Add(parsed)
                    Catch ex As Exception
                        Console.WriteLine(String.Format("Error! `{0}` is not a valid number or operator!", currentInput))
                        Continue While
                    End Try
            End Select
        End While
    End Sub
End Module