I saw the question “How to add leading zeros to a number” on the ASP.NET forums countless times before. And often the answers provide solutions that work, but are overkill as well.
The two cleanest methods I know are String.Format and PadLeft.
1: Console.WriteLine("Using .ToString()");
2: Console.WriteLine(String.Format("{0:0000}", 16));
3:
4: Console.WriteLine("-------------------");
5:
6: Console.WriteLine("Using .PadLeft()");
7: Console.WriteLine(Convert.ToString(16).PadLeft(4, '0'));
You can see the result here.
//Using .ToString()
//0016
//-------------------
//Using .PadLeft()
//0016