I cant get the loop right

Ok I have got this far and if you run it, it will do what you ask. Now when I type in 99999 or -99999 it will not end. Can someone tell me what I am doing wrong. I am suppose to loop until a sentinel value of -99999 is enter for previous meter reading.

 Sub Main()
    ' program to compute a consumer’s electric bill. It will calculate the bill for one or more customers 
    ' by looping until a sentinel value of -99999 is entered for the previous meter reading.
    Dim previousReading As Integer = 0
    Dim currentReading As Integer = 0
    Do While (previousReading <> -99999)
        Dim salesTax As Double
        ' prompt user to input value for previous reading then convert to integer
        Console.WriteLine("Enter the value of previous meter reading")
        previousReading = Convert.ToInt32(Console.ReadLine(开发者_C百科))
        ' prompt user to input value for current reading then convert to integer
        Console.WriteLine("Enter the value of current meter reading")
        currentReading = Convert.ToInt32(Console.ReadLine())
        Dim kwhConsumed As Integer
        Dim electricCharge, totalBill As Double
        ' calculate KWH consumed
        kwhConsumed = currentReading - previousReading
        ' Use select case to determine electricCharge
        Select Case kwhConsumed
            Case Is < 500
                electricCharge = kwhConsumed * 0.05
            Case 500 To 1000
                electricCharge = 25 + ((kwhConsumed - 500) * 0.055)
            Case Is > 1000
                electricCharge = 52.5 + ((kwhConsumed - 1000) * 0.06)
        End Select
        ' calculate sales tax
        salesTax = electricCharge * 0.085
        ' calculate total charges
        totalBill = electricCharge + salesTax
        ' Output values for kwhConsumed, electricCharge, salesTax, and totalBill
        Console.WriteLine("KWH consumed = " & kwhConsumed & " KWH")
        Console.WriteLine("Electric charge = $" & Math.Round(electricCharge, 2))
        Console.WriteLine("Sales tax = $" & Math.Round(salesTax, 2))
        Console.WriteLine("Total bill = $" & Math.Round(totalBill, 2))
    Loop
End Sub

You can try using string comparison instead for previousReading <> -99999. You also need to use absolute value to consider both -99999 and 99999. Do something like this

Do While (previousReading <> 99999) 

    //code
  previousReading = Math.Abs(Convert.ToInt32(Console.ReadLine()))
    //code

Loop

I'm guessing this is homework?

Instead of blurting out the answer, I wonder if you might think about inserting a Debug.Print statement and some kind of "break" statement after your previousReading = Convert.ToInt32 statement. To look for the "break" statement, search for "vb.net exit loop" and see what pops up.