Problems with Inputbox

[jmcilhinney]

The primary problem with InputBox is that it exists. You should basically avoid using it if you possibly can. If you have to use it because the assignment says so, which I suspect is the case here, then you are stuck. Otherwise, you should create your own form that matches the rest of your UI and display it as a modal dialogue.

Assuming that you must use InputBox then here is some pseudo-code:

Do
    Call InputBox and get result

    If result is empty
        Exit Do
    Else
        Try to convert input to number and use as required
    End If
Loop

Unless you have been told that you can assume that the user input will always be a valid number, you should be using Decimal.TryParse to validate and convert rather than CDec, which will throw an exception if the data is not a valid number.