Private Shared Function subtractMonth(ByVal evaluationDate As DateTime) As DateTime
    Dim s As StringBuilder = New StringBuilder

    s.Append(evaluationDate.Year.ToString())
    s.Append("-")
    s.Append(evaluationDate.Month.ToString())
    s.Append("-01")

    Return Convert.ToDateTime(s.ToString()).AddDays(-1)
End Function

This is clearly .NET code (VB.NET). So, the developer would have the whole framework to their disposal, including the operations that already built into the DateTime class (or, wait, it's a struct, isn't it?). For example, DateTime.Subtract. Or heck, there is even an overloaded operator, "-" to do subtraction. Unfortunatly I also see this kind of floating by every now and then at college.. and remember I'm in the third year (out of four) of a Computer Science major.

As an aside, this code would probably cause bugs on platforms (seeing as Convert.ToDateTime probably uses the default date/time settings for that particular Windows install) where the date format isn't Y-M-D (such as Dutch systems, where the date format is D-M-Y). Oh, and also, some people start abusing the StringBuilder class after hearing it is more effecient. Seriously, don't use if you're just concatting two or three strings.

The trouble is you think you have time
Enough to waste enough to embrace
Enough to let you just talk about what you will do
Totally lost, fully undone
How do you change what you've become?

It's all change now
Do the best you know how
When desire ends
Peace will come again

The trouble is you think you'll find
Why should you try what you don't know
You have a description of the world that you believe
But will all let you down
It always lets you down

It's all change now
Do the best you know how
When desire ends
Peace will come again

So do it now, do it well
Tomorrow all will have changed again
Be awake, be amazed
Be a guest at the best parade

For it's all change now
Do the best you know how
When desire ends
Peace will come again
It's all change
Oh it's all change
It's all change
Change