How should I check if a .NET decimal value is a whole number?

Question

I have class representing a unit of measure with a Decimal as the numeric. Just to simplify things for this example, let's say I'm representing centimeters. I'd like to implement a ToString() method for this class. The thing is, if the numeric value is a whole number I'd like to just display the decimal as an integer. Otherwise, I'd like to keep it as a decimal. So, for example, 10.5D centimeters would display as "10.5cm", but 7.0D centimeters should display as "7cm". I'd like this to be fast and simple to read. I have a working solution, but it seems like there should be a better way.

Here's a contrived example showing my first crack at it:

Public Property Units As String = "cm"
Public Property NumericValue As Decimal = 10.5D

Public Overrides Function ToString()
   Dim num As String = If(Me.NumericValue = Decimal.Ceiling(Me.NumericValue), _
                          Decimal.ToInt32(Me.NumericValue).ToString(), _ 
                          Me.NumericValue.ToString())
   Return num + Me.Units
End Function

I'm a little uncomfortable with Me.NumericValue = Decimal.Ceiling(Me.NumericValue). Any thoughts on how to do this better? Is there something I could do with String.Format or some other method on the Decimal class that would make this clearer and keep it performant?

Answer 1

You can try:

decimal.Truncate(myDecimal) == myDecimal

This might be good enough for your purposes. However, this a complex issue; simply using System.Decimal does not get rid of all problems related to floating-point representations. The code-sample here is a case in point.

Answer 2

Here's another way

    Public Overrides Function ToString() 
        If (Me.NumericValue - Math.Round(Me.NumericValue, 0) > 0) Then
                Return String.Format("{0:###,###,##0.00}{1}", Me.NumericValue, Units);
        Return String.Format("{0:###,###,##0}{1}", Me.NumericValue, Units)
    End Function

Answer 3

Are you sure you want to do this?

Anyone with an enginerring background will read "7cm" as "approx. seven centimeters" and "7.00cm" as "seven centimetres to the nearest millimeter".