CODEWITHSUNDEEP
c#random
Rainy267
Rainy267

Reputation: 61

Random seed c# - How to generate same sequence of numbers for debug

I am writing a cards game, and need to draw random cards from pile. I am using Random and Random.Next(..) for that. Now I want to debug my application, and want to be able to reproduce certain scenarios by using the same Random sequence. Can anyone help...? I couldn't find an answer over several searches. Thanks.

Upvotes: 4

Views: 4371

Answers (5)

Rotem
Rotem

Reputation: 21927

Use the overload of the Random constructor which accepts a seed value

static Random r = new Random(0);

This will produce the same sequence of pseudorandom numbers across every execution.

Upvotes: 11

AlanT
AlanT

Reputation: 3663

Possibly a bit of overkill for this case (using a seed will give you repeatability) but a good shape for dealing with dependencies over which you do not have full control is to wrap the dependency and access it through an interface. This will allow you to swap in a version that gives specified behaviour for unit testing/ debugging.

e.g.

public interface IRandom {
    int Get();
}

public class DefaultRandom : IRandom {
    private readonly Random random;

    public DefaultRandom() {
        random = new Random();
    }

    public int Get() {
        return random.Next();
    }
}

public class TestRandom : IRandom {

    private readonly List<int> numbers;
    private int top;

    public TestRandom() {
        numbers = new List<int> {1, 1, 2, 3, 5, 8, 13, 21};
        top = 0;
    }

    public int Get() {
        return (top >= numbers.Count)
                ? 0
                : numbers[top++];
    }
}

One of the nice aspects of this method is that you can use specific values (say, to test edge cases) which might be hard to generate using a fixed seed value.

Upvotes: 1

Bathsheba
Bathsheba

Reputation: 234715

You will need to seed your random number generator. Assuming you're using System.Random, use

Random r = new Random(<some integer>);

which starts the sequence at <some integer>.

But an important note here: you will need to research your random number generator carefully. Else it will be possible to decipher your sequence which will make playing your game unintentionally profitable for an astute user. I doubt you'll be using Random once you pass to production. (Technically it's possible to decipher a linear congruential sequence - which is what C# uses - in a little over three drawings.)

Upvotes: 4

Georgi Karadzhov
Georgi Karadzhov

Reputation: 771

Use the same seed in Random constructor. That guarantee you that Next() will give the same results. For example 

Random randomGen1 = new Random(5);

Random randomGen2 = new Random(5);

int r1 = randomGen1.Next();
int r2 = ramdomGen2.Next();

if(r1 == r2)
{
 Console.WriteLine("Great success!!");
}

Upvotes: 1

knittl
knittl

Reputation: 265241

Create a System.Random instance with the same seed:

Random random = new System.Random(1337);

Upvotes: 1

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