CODEWITHSUNDEEP
c#random
Edward Tanguay
Edward Tanguay

Reputation: 193352

What is the easiest way to generate quasi random numbers in C#?

All I want is a pragmatic random number generator in C# so I can say e.g. 

int dummyAge = MathHelpers.GetRandomNumber(20,70);

and have it seem quasi random, e.g. to generate dummy data.

Most stack overflow questions on this topic and on the web get into a philosophical discussions on true randomness which is not what I'm interested at the moment, e.g. I did one in PHP a long time ago which uses milliseconds/sleep which is fine for dummy data, I'm just trying to do this in C# quick.

Does anyone have a quick half-decent C# random number generator based on some time seed, etc. or, how could I change the following code so that it always doesn't generate the same 5 number in a row?

using System;

namespace TestRandom23874
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("the random number is: {0}", MathHelpers.GetRandomNumber(1, 10));
            Console.WriteLine("the random number is: {0}", MathHelpers.GetRandomNumber(1, 10));
            Console.WriteLine("the random number is: {0}", MathHelpers.GetRandomNumber(1, 10));
            Console.WriteLine("the random number is: {0}", MathHelpers.GetRandomNumber(1, 10));
            Console.WriteLine("the random number is: {0}", MathHelpers.GetRandomNumber(1, 10));
            Console.ReadLine();
        }
    }

    public class MathHelpers
    {
        public static int GetRandomNumber(int min, int max)
        {
            Random random = new Random();
            return random.Next(min, max);
        }
    }
}

Upvotes: 8

Views: 2206

Answers (2)

Jon Skeet
Jon Skeet

Reputation: 1502016

BFree's answer is fine, but I think it's also worth mentioning a slightly different pattern - passing the Random instance into anything that needs it, rather than always using a single instance via a static variable. The downside of the latter approach is that Random isn't thread-safe. You either need some locking, or thread-local variables, or avoiding using multiple threads to start with. So I would adjust the original code in the question to:

using System;

namespace TestRandom23874
{
    class Program
    {
        static void Main(string[] args)
        {
            Random rng = new Random();
            Console.WriteLine("the random number is: {0}", 
                MathHelpers.GetRandomNumber(rng, 1, 10));
            Console.WriteLine("the random number is: {0}", 
                MathHelpers.GetRandomNumber(rng, 1, 10));
            Console.WriteLine("the random number is: {0}", 
                MathHelpers.GetRandomNumber(rng, 1, 10));
            Console.WriteLine("the random number is: {0}", 
                MathHelpers.GetRandomNumber(rng, 1, 10));
            Console.WriteLine("the random number is: {0}", 
                MathHelpers.GetRandomNumber(rng, 1, 10));
        }
    }

    public class MathHelpers
    {
        public static int GetRandomNumber(Random random, int min, int max)
        {
            return random.Next(min, max);
        }
    }
}

It's just basic inversion of control, really. You might have one static RNG with locking round it, used to generate a new instance of Random in a thread-safe way when you need it (by randomly generating a seed and then using that to create the instance) then reusing the Random throughout a particular single-threaded set of operations.

Upvotes: 2

BFree
BFree

Reputation: 103750

public class MathHelpers
    {
        private static Random random = new Random();
        public static int GetRandomNumber(int min, int max)
        {
            return random.Next(min, max);
        }
    }

This way, you're not creating a new Random object every time, rather you're reusing the same one. When you recreate a new one quickly enough, they will yield the same results. If however, you reuse an existing one, you'll get randomness.

Upvotes: 13

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