Category Archives: .NET

Calculate age (for instance, on reference data)

Now and then, I have to calculate ages (for instance, on a reference date). The method to calculate ages in .NET is pretty simple, although it can be ‘a pain in the ass’ to find out how simple it should have been :) … Enjoy the code :) !

public static class DateTimeHelper
    public static int CalculateAge(DateTime birthday)
        return CalculateAge(DateTime.Now, birthday);

    public static int CalculateAge(DateTime referenceDate, DateTime birthday)
        // calculate age in years on the given reference date.
        var comparisonDate = new DateTime(birthday.Year, referenceDate.Month, referenceDate.Day);

        return (comparisonDate.Date < birthday.Date)
                      ? referenceDate.Year - birthday.Year - 1
                      : referenceDate.Year - birthday.Year;

Dutch bank account number check

For a Dutch customer I currently work for, I worked out the bank account number check (in Dutch: elfproef voor bankrekeningnummers). After checking out the Internet for the correct definition of Dutch bank account numbers (found on Wikipedia), I created the next check in C#:

var cleanAccNumber = accountNumber.Replace(".", "");

// A bank account number consists of 9 or 10 digits
if (!(cleanAccNumber.Length == 9 || cleanAccNumber.Length == 10)) return false;

// ... all being numeric and not resulting in a 0 when converted to a number ...
long l;
if (!long.TryParse(cleanAccNumber, out l)) return false;
if (l == 0) return false;

// pad it to the left to 10 digits with preceding zero's.
cleanAccNumber = cleanAccNumber.PadLeft(10, '0');

// ... the number must be validatable to the so-called 11-proof ...
long total = 0;
for (var i = 1; i <= cleanAccNumber.Length; i++)
// 11-proof for 10 digit bank account numbers (bron: Wikipedia): (1*A + 2*B + 3*C + 4*D + 5*E + 6*F + 7*G + 8*H + 9*H + 10*I) % 11 == 0
var number = Convert.ToInt32(cleanAccNumber[i - 1].ToString());
total += number*i;

// ... not result in a 0 when dividing by 11 ...
if (total == 0) return false;

// ... and not have a modulo when dividing by 11.
return total % 11 == 0;

Good luck when you should build one for yourself!

How to insert blank rule (<br />) from C# code

Once in a while I have to develop custom user controls that require blank rules in them. Almost always I think again: ‘I should have blogged about it, would have saved me lots of time searching’ :) … Well, no more, because here it is…

Many people using blank rules in C# code, use the following commands:

var brControl1 = new HtmlGenericControl { InnerHtml = "<br />" };
var brControl2 = new HtmlGenericControl("br");

However, brControl1 also prints a <span> tag and brControl2 prints <br></br>. Both options are not really useful. You should take notice of the fact that the HtmlGenericControl is not meant to be used for anything else than span, body, div and font (what is designed for ‘as the word goes’).  The way to go when printing a blank rule is:

var brControl3 = new LiteralControl("<br />");

This actually prints exactly what you would like it to print, namely <br />. Hope this helps you too :) ! BTW, if you are using the HtmlTextWriter class, you can also use the WriteBreak() function if you like.

Solution: The operation could not be completed. Invalid FORMATETC structure

This morning I ran into a ASP.NET bug in Visual Studio. Dragging a custom server control on an aspx file was not possible since I had ‘an invalid FORMATETC structure’ (what the …. is that?!). The message box alerting me something is really really wrong is this one:


Trying to solve the bug, I  found the following attribute to be the problem: [ToolboxItem(true)]. Just delete the attribute, rebuild the application and the problem/bug disappears!

Good luck! Happy coding!

How to detect installed CLR versions and how they are used…

It has been a while since I posted anything on my blog. Sorry for keeping you on hold ;) ! I think the blog will be filled with some information shortly, since I am still overthinking all the great stuff I saw on Tech-Ed North America a couple of weeks ago (first I had to overcome the jetlag, then the weather in The Netherlands, etc. etc. :) ). Enough nonsense for now!

While attending a session by Scott Hanselman on everything new in .NET 4.0 he showed a wonderful small tip, not only useful for the few of us already working on Visual Studio 2010: when working in the VS.NET Command Prompt, there is a small but useful command called ‘CLRVER’. It shows all .NET versions installed on your computer. Also, as an addition to this command, you can show active runtime processes using the -all switch. Nice piece of code! Enjoy!