Those of us who lived through Y2K remember that, after all was said and done, it was little more than an inconvenience. Fix a couple of reports displaying “19100” here and correct some validation logic there. Although Sherman wasn’t there to experience all of the Y2K fun, as a maintenance programmer, he has had the pleasure of experiencing exactly what it was like, each and every year.

In fact, his very first assignment was to fix a Y2.007K bug in an application developed the previous year: the original developer simply hard-coded 2006 as the year. And it wasn’t the only Y2.007 bug.

2008 introduced a whole slew of problems, but most of the problems had an easy work-around: just wait until March 1st. It’s not that the developers didn’t know about the leap year, it’s just they had very often implemented the logic incorrectly.

Last year (2010) was a bigger than he figured, one, as several developers (many just copy/pasting from each other) believed you could simply take the last digit of the year and increment it to find the next year... leaving the current year as 2000 or 20011.

And sadly, this year was no different. One of the very first tickets of 2011 was a high-priority, fix-by-January-2nd issue that centered around the following code.

Function CheckValidDate(thisDate As String)
    CheckValidDate = True
    Dim thisChar As String
    Dim i As Integer
    
    Dim slashCount As Integer
    Dim dayStr As String
    Dim monthStr As String
    Dim yearStr As String
    
    Dim myAsc As Long
    
    For i = 0 To Len(thisDate) - 1
        thisChar = Left(thisDate, i + 1)
        thisChar = Right(thisChar, 1)
        
        myAsc = Asc(thisChar)
        
        If (thisChar = "/") Then
            slashCount = slashCount + 1
        ElseIf (slashCount = 0) Then
            monthStr = monthStr & thisChar
        ElseIf (slashCount = 1) Then
            dayStr = dayStr & thisChar
        Else
            yearStr = yearStr & thisChar
        End If
        
        
        If ((myAsc < 47 Or myAsc > 57) And myAsc <> Asc("/")) Then
            CheckValidDate = False
        End If
    Next
    
    If (slashCount <> 2) Then
        CheckValidDate = False
    End If
    
    If (CheckValidDate = True) Then
        Dim dayInt As Integer
        Dim monthInt As Integer
        Dim yearInt As Integer
        dayInt = CInt(dayStr)
        monthInt = CInt(monthStr)
        yearInt = CInt(yearStr)
        
        If (monthInt < 1 Or monthInt > 12) Then
            CheckValidDate = False
            
        ElseIf (monthInt = 2) Then
            If (dayInt > 28 And yearInt Mod 4 <> 0) Then
                CheckValidDate = False
            ElseIf (dayInt > 29 And yearInt Mod 4 = 0) Then
                CheckValidDate = False
            End If
        
        ElseIf ((monthInt = 4 Or monthInt = 6 Or monthInt = 9 Or monthInt = 11) And dayInt > 30) Then
            CheckValidDate = False
        
        ElseIf (dayInt > 31) Then
            CheckValidDate = False
        End If
        
        If ((yearInt > 10 And yearInt < 100) Or (yearInt > 100 And yearInt < 2000) Or (yearInt > 2010)) Then
            CheckValidDate = False
        End If
        
    End If
    
End Function

Sherman replaced the entire method body with CheckValidDate = IsDate(thisDate).