random - Using Randomize() before Rnd() in VB.NET

Question

I have previously been told that I should always use Randomize() before I use Rnd() in a VB.NET application. Yet, it always seems to work fine without it. What does adding Randomize() do for me in this case?

It doesn't appear to affect my application in the least.

Answer 1

In Visual Basic, Rnd() uses a mathematical operation to produce the next "random" number. Because the actual operation is known, given a specific value, you can predict the next value. However, given an arbitray start value the numbers have good distribution - these are "pseudo-random" numbers.

To keep Rnd() from startng at a predictable number (and hence giving the same sequence of "random" numbers every time), Randomize() should be called to use the machine clock to set the initial value (called a seed).

(In the .NET world, I'd use System.Random instead if you can.)