Random.Next returns always the same values [duplicate]

Question

This is really weird, and I cannot see why this is happening. In the foreach cycle, I am iterating through a class A collection, and for each class, I call the Count() method, where r1 and r2 numbers are generated from range [-1,1]. The problem is that Random.Next returns the same "random" numbers for each instance. When the results for the first instance are 0 and -1, the same ones will be returned from following instances. Please, could you tell me why this is happening? Also, I cannot get different results in each class A instance. This is the code:

class a {  Random rnd = new Random();  private void Count()  {   int r1 = rnd.Next(-1, 1);   int r2 = rnd.Next(-1, 1);  } } class b {  List<a> listofA=new list<a>();  foreach (a ACLASS in listofA)  {   ACLASS.Count();  } } 

Answer 1

The problem is that you are creating instances of the Random class too close in time.

When you create a Random object, it's seeded with a value from the system clock. If you create Random instances too close in time, they will all be seeded with the same random sequence.

Create a single Random object and pass its reference to the constructor when you create instances of the "a" class, instead of creating one Random object for each "a" instance.

Answer 2

Use a single, static Random number generator for all instances of the class.

class a {   private static Random rnd;   static a() {       rnd = new Random();   }   private void Count()   {     int r1 = rnd.Next(-1, 2);     int r2 = rnd.Next(-1, 2);   } } 

Note the change to give you numbers in the range -1,1 rather than -1,0