How to Generate Random Numbers (integers or long) in C#

Random numbers are widely used in Digital games, Statistical Sampling, Cryptography, computations in statistical physics,numerical analysis,Radio communications and casino games like Roulette wheel etc.

We can use Random class to Generate Random Numbers in C#.

What is C# Random Class? #

C# Random class is a pseudo-random number generator, which is an algorithm that generates a sequence of numbers that meet certain statistical requirements for randomness.

This class has 5 methods Next(), NextInt64(),NextBytes(), NextDouble() and NextSingle().

Depending upon on the type of Number i.e., int,long etc we can use corresponding method.

Let’s go through the examples to understand it further.

Generate Random integer in C# #

Steps to generate Random integer in C#

1. Instantiate random number class.
2. Use Random.Next() method to return random integer between Int32.MinValue and Int32.MaxValue.

var randomInteger = new Random();

randomInteger.Next();
randomInteger.Next();
randomInteger.Next();
randomInteger.Next();
randomInteger.Next(); 


/* OUTPUT : 
2027076668
1095111085
535874255
1973884472
430547700
*/

Generate Random integer between minimum and maximum values #

Random.Next() has an overloaded method, which accepts minimum and maximum values as parameters which generates a random integer between the given values.

To generate random numbers between 100 to 1000 use the below code

Console.WriteLine("Five random integers between 100 and 1000");

for (int counter = 0; counter <= 4; counter++)
    Console.WriteLine("{0}", randomNumber.Next(100, 1000));

/* OUTPUT:
Five random integers between 100 and 1000
904
853
554
290
614
*/

Generate Random long number(Int64) in C# #

To generate Random long number i.e, Int64 in C#, Use Random.NextInt64() method which returns random Int64 number between Int64.MinValue and Int64.MaxValue.

var RandomInt64 = new Random();

RandomInt64.NextInt64();
RandomInt64.NextInt64();
RandomInt64.NextInt64();
RandomInt64.NextInt64();
RandomInt64.NextInt64(); 


/* OUTPUT : 
5200810282391000059
6501337495320049889
6318562423063201438
3733878081804548122
8421209223603063849
*/

Generate Random long number(Int64) in Given Range #

Similar to Random.Next(), Random.NextInt64() has an overloaded method, which accepts Range i.e., minimum and maximum values as parameters which returns a random Int64 number between them.

To generate random numbers between 100000 to 200000 use the below code

var RandomInt64 = new Random();


Console.WriteLine("Five random integers between 100000 and 200000");

for (int counter = 0; counter <= 4; counter++)
    Console.WriteLine("{0}", RandomInt64.NextInt64(100000, 200000));

/* OUTPUT:
Five random long Int64 numbers between 100000 and 200000
144220
194475
185075
159433
136542
*/

The generated random numbers are not completely random because a mathematical algorithm is used to select them, but they are good enough for most of the real world cases.

Avoiding duplicates while generating random numbers #

If you are initializing more than one new Random() class.

You might get duplicates random numbers. (Multithreaded application)

var randomOne = new Random();
var randomTwo = new Random(); // Don't do this

So it’s better to initialize only one Random() class instance, and use it across the application.

//Function to generate unique random number using `Random()` class

private static readonly Random randomInstance = new Random();

public static int GenerateRandomNumber(int min, int max)
{
    lock(randomInstance) // synchronize
    {
        return randomInstance.Next(min, max);
    }
}

If you want to generate series of random numbers, in multithreaded environment use above method.

Using cryptographic C# RandomNumberGenerator #

If you want to generate truly unique random numbers you can make use of RandomNumberGenerator class which is part of System.Security.Cryptography library.

This class generates a cryptographically secure random number and suitable for creating a random password.

var randomNumber= RandomNumberGenerator.GetInt32(Int32.MaxValue);

We can also pass range to the RandomNumberGenerator method.

var randomNumber= RandomNumberGenerator.GetInt32(2000,5000);

Using C# RNGCryptoServiceProvider class #

This class is obsolete now, Don’t use this method.

RNGCryptoServiceProvider implements a cryptographic Random Number Generator (RNG) using the implementation provided by the cryptographic service provider (CSP).

Use the below code create a random number with the C# RNGCryptoServiceProvider class.

using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
{
   byte[] randomNumber = new byte[4];//4 for int32
   rng.GetBytes(randomNumber);
   int value = BitConverter.ToInt32(randomNumber, 0);
}

Summary #

In this tutorial we learnt different ways to generate random numbers in C# with simple examples.