Generate random values in C#

Question

How can I generate random Int64 and UInt64 values using the Random class in C#?

Answer 1

You can use bit shift to put together a 64 bit random number from 31 bit random numbers, but you have to use three 31 bit numbers to get enough bits:

long r = rnd.Next();
r <<= 31;
r |= rnd.Next();
r <<= 31;
r |= rnd.Next();

Answer 2

You could create a byte array, fill it with random data and then convert it to long (Int64) and ulong (UInt64).

byte[] buffer = new byte[sizeof(Int64)];
Random random = new Random();

random.NextBytes(buffer);
long signed = BitConverter.ToInt64(buffer, 0);

random.NextBytes(buffer);
long unsigned = BitConverter.ToUInt64(buffer, 0);

Answer 3

You don't say how you're going to use these random numbers...keep in mind that values returned by Random are not "cryptographically secure" and they shouldn't be used for things involving (big) secrets or (lots of) money.

Answer 4

Random r=new Random();
int j=r.next(1,23);
Console.WriteLine(j);

Answer 5

Use Random.NextBytes() and BitConverter.ToInt64 / BitConverter.ToUInt64.

// Assume rng refers to an instance of System.Random
byte[] bytes = new byte[8];
rng.NextBytes(bytes);
long int64 = BitConverter.ToInt64(bytes, 0);
ulong uint64 = BitConverter.ToUInt64(bytes, 0);

Note that using Random.Next() twice, shifting one value and then ORing/adding doesn't work. Random.Next() only produces non-negative integers, i.e. it generates 31 bits, not 32, so the result of two calls only produces 62 random bits instead of the 64 bits required to cover the complete range of Int64/UInt64. (Guffa's answer shows how to do it with three calls to Random.Next() though.)

Answer 6

Here you go, this uses the crytpo services (not the Random class), which is (theoretically) a better RNG then the Random class. You could easily make this an extension of Random or make your own Random class where the RNGCryptoServiceProvider is a class-level object.

using System.Security.Cryptography;
public static Int64 NextInt64()
{
   var bytes = new byte[sizeof(Int64)];    
   RNGCryptoServiceProvider Gen = new RNGCryptoServiceProvider();
   Gen.GetBytes(bytes);    
   return BitConverter.ToInt64(bytes , 0);        
}