3 digit random number in C#

Question

Is there a better way to generate 3 digit random number than the following:

var now = DateTime.Now.Ticks.ToString(CultureInfo.InvariantCulture);
string my3digitrandomnumber = now.Substring(now.Length - 7, 3);

Thanks..

Answer 1

Yes - your current code isn't random at all. It's based on the system time. In particular, if you use this from several threads at the same time - or even several times within the same thread in quick succession - you'll get the same number each time.

You should be using Random or RandomNumberGenerator (which is more secure).

For example, once you've got an instance of Random, you could use:

int value = rng.Next(1000);
string text = value.ToString("000");

(That's assuming you want the digits as text. If you want an integer which is guaranteed to be three digits, use rng.Next(100, 1000).)

However, there are caveats around Random:

• You don't want to create a new instance each time you use it; that would also be time based unless you specify a seed
• It's not thread-safe

So ideally you probably want one per thread. My article on randomness talks more about this and gives some sample code.

Answer 2

int r = (new Random()).Next(100, 1000);