How do you specify a negative step for an unsigned integer index in a VB.net for-loop

Question

How do you specify a negative step on a unsigned integer index for a for-loop in VB.net

The following code will not compile:

Option Strict

For i as uLong = uLong.maxvalue To 0 Step -1UL
  ...
next i

Gives this: Error: BC30439 Constant expression not representable in type 'ULong'

Answer 1

A unsigned Int16/Int32/Int64 cannot be represented as negative value, there is no way to do that, see ULong.MinValue.

You have two options here:

• 1. Simulatte a negative step by using a while/until loop:

     Dim i As ULong = ULong.MaxValue
     
     While (i <> ULong.MinValue)
         Console.WriteLine(i)
         i -= 1UL ' Decrement current value by desired amount.
     End While
     

• 2. Set the /removeintchecks vb's compiler parameter, then you can use negative values for unsigned datatypes.

     Note that you can set this parameter in a guided way trough the configuration page of the solution, in the "Advanced Compile Options", check "Remove Integer Overflow Checks".