Generate random values in C#

Question

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

Answer 1

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);        
}

Answer 2

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

Another answer with RNGCryptoServiceProvider instead of Random. Here you can see how to remove the MSB so the result is always positive.

public static Int64 NextInt64()
{
    var buffer = new byte[8];
    new RNGCryptoServiceProvider().GetBytes(buffer);
    return BitConverter.ToInt64(buffer, 0) & 0x7FFFFFFFFFFFFFFF;
}

Answer 4

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

Answer 5

I always use this to get my random seed (error checking removed for brevity):

m_randomURL = "https://www.random.org/cgi-bin/randnum?num=1&min=1&max=1000000000";
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(m_randomURL);
StreamReader stIn = new StreamReader(req.GetResponse().GetResponseStream());
Random rand = new Random(Convert.ToInt32(stIn.ReadToEnd()));

random.org uses atmospheric noise to generate the randomness and is apparently used for lotteries and such.

Answer 6

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();