What's available?

Xojo®'s API provides us with three ways to convert a decimal number to a whole number:

  • Round():
    It rounds a Double to the nearest whole number. Round( 18.35 ) returns 18 while Round( 18.55 ) returns 19.
  • Floor():
    It returns the next lowest whole number. Floor( 14.6 ) returns 14 and Floor( -14.6 ) returns -15.
  • Ceil():
    It returns the next highest whole number. Ceil( 14.6 ) returns 15 and Ceil( -14.6 ) return 14.

But if you only need to truncate a decimal number to its integer part, there is no out-of-the-box method. So let's implement our own truncate method.

Implementing Trunc()...

If the number to truncate is positive then we'll use Floor() and if the number is negative, we'll use Ceil(). For the '0' (zero) case, we'll just consider it as a positive number. Let's add the following code to a module as a public method:

Function Trunc(inValue As Double) As Double
  If inValue >= 0.0 Then
    Return Floor( invalue )
    Return Ceil( inValue )
  End If
End Function

And you can use it like this:

Dim theWholeNumber As Double = Trunc( 1234.567 )
MsgBox Str( theWholeNumber )

...and Double.Trunc()

While we're at it, let's extend the Double data type with a Double.Trunc() As Double method. So in the same module, create a new Trunc() method defined like this:

Function Trunc(Extends extValue As Double) As Double
  If extValue >= 0.0 Then
    Return Floor( extValue )
    Return Ceil( extValue )
  End If
End Function

Now you can use it like this:

Dim theDecimalNumber As Double = 1234.567
Dim theWholeNumber As Double = theDecimalNumber.Trunc
MsgBox Str( theWholeNumber )

Going further

I wrote these methods as I needed to determine if a Double was a whole number or not. For that purpose, I choose to compare the Double number and its truncated counterpart. If they're equals, then this is a whole number. Otherwise, it's a decimal number.

Function IsWholeNumber(inValue As Double) As Boolean
  Return inValue.Equals( inValue.Trunc, 0 )
End Function

And the Double.IsWholeNumber() As Boolean syntax:

Function IsWholeNumber(Extends extValue As Double) As Boolean
  Return extValue.Equals( extValue.Trunc, 0 )
End Function

The use of Equals() allows us to get rid of the "Performing a = comparison [...] can yield unexpected result [...]" warning. If you want, I leave it to you to implement a IsOdd( Double ) As Boolean.


As always, Xojo® gives us the opportunity to expand its API with our own functionalities. In the same spirit, you can add a IsOdd( Double ) As Boolean and a Double.IsOdd() As Boolean and even transpose them to handle the Single data type.