Question

How do you generate random numbers effectively?
Every time a random number program boots up, it starts spitting same numbers as before. (I guess because of quasi nature of random number generation)
Is there a way, that random# generation becomes non-deterministic? sort of Entropy addition to generation that number generated after boot is in different sequence than last one. (random random rather that quasi-random)
Also, say range of such generation is (m,n) such that n-m = x, is there a chance that a number say ‘p’ appears next time after x-1 other numbers have been generated. But next lot of such x numbers would not be same as sequence from last one. Example:
range: 1,5. Generation : 2,4,5,1,3 (1st) 4,2,3,1,5 (2nd)… same numbers.
I out of nonplussed state of mind wrote this :

int num1 = (rand.Next(1, 440) *31* (int)DateTime.Now.Ticks *59* (DateTime.Now.Second * 100) % 439) + 1;
int num2 = (rand.Next(1, 440) *31* (int)DateTime.Now.Ticks *59* (DateTime.Now.Second * 100) % 439) + 1;

here range was (1,440). but it still generates numbers out of bound and zero, and it’s frequency is not that great either. It is C#.NET code. Why so?

your answers can be language agnostic / algorithmic / analytical. Thanks in advance.

Answer 1

Very few “random” number generators are actually random. Almost all are pseudorandom, following a predictable sequence when started with the same seed value. Many pseudorandom number generators (PRNGs) get their seed from the date and time of their initial invocation. Others get their seed from a source of random data supplied by the operating system, which often is generated from outside sources (e.g., mouse motion, keyboard activity).

The right way to seed a good random number generator is to not seed it. Every good generator has a default mechanism to supply the seed, and it is usually much better than any you can come up with. The only real reason to seed the generator is if you actually want the same sequence of random numbers (e.g., when you’re trying to repeat a process that requires randomness).

See http://msdn.microsoft.com/en-us/library/system.random.aspx for the details of the C# Random class, but basically, it uses a very well known and respected algorithm and seeds it with the date and time.

To answer your key question, just use rand.Next(min, max+1) and you’ll always get a random sequence of numbers between min and max inclusive. The sequence will be the same every time you use the same seed. But rand = new Random() will use the current time, and as long as your program is invoked with some separation in time, they’ll be different.