how to generate unique random number

Xaska Dadu

using System; namespace G06_20201027 { class Program { static void Main() { Random r = new Random(); int[] x = new int[10]; for (int i = 0; i < x.Length; i++) { x[i] = r.Next(15); } for (int i = 0; i < x.Length; i++) { Console.WriteLine(x[i]); } Console.ReadKey(); } } }

4 Replies

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Rajanikant Hawaldar5y ago
Hello Xaska Dadu, could you check below code.
using System;
namespace G06_20201027
{
    class Program
    {
        static void Main()
        {
            int[] x = new int[10];
            Random r = new Random();
            for (int i = 0; i < x.Length; i++)
            {
                var next = 0;
                while (true)
                {
                    next = r.Next(10);
                    if (!Contains(x, next)) break;
                }
                x[i] = next;
                Console.WriteLine(x[i]);
            }
            Console.ReadKey();
        }
        static bool Contains(int[] array, int value)
        {
            for (int i = 0; i < array.Length; i++)
            {
                if (array[i] == value) return true;
            }
            return false;
        }
    }
}
+1
Sachin Singh5y ago
C# Random Method uses your CPU clock as seed , so it is very much insecure and hackable, better is to use RNGCrypto
if you only want to generate integers then your code should be
using System.Security.Cryptography;
static void Main(string[] args)
     {
         Random random = new System.Random();
         int value = random.Next(0, 100); //returns integer of 0-100


         Console.WriteLine(value); // unsecure and not unique


         RNGCryptoServiceProvider provider = new RNGCryptoServiceProvider();
         var byteArray = new byte[4];
         provider.GetBytes(byteArray);

         //convert 4 bytes to an integer
         var randomInteger = BitConverter.ToUInt32(byteArray, 0);




         Console.WriteLine(randomInteger); // secure and unique

             Console.ReadLine();


     }
+1
Xaska Dadu5y ago
thanks Sachin Singh but i'm bit confused with your code can you explain bit more? sorry im newb right now but thanks alot for attention
+1
Sachin Singh5y ago
Unsecure Random Nums
Random random = new System.Random();
int value = random.Next(0, 100); //returns integer of 0-100
double value2 = random.NextDouble(); //returns floating point 0.0-1.0

var byteArray = new byte[256];
random.NextBytes(byteArray); //fill with random bytes
secure Random Nums (Unique)
RNGCryptoServiceProvider provider = new RNGCryptoServiceProvider();
var byteArray = new byte[4];
provider.GetBytes(byteArray);

//convert 4 bytes to an integer
var randomInteger = BitConverter.ToUInt32(byteArray, 0);

var byteArray2 = new byte[8];
provider.GetBytes(byteArray2);

//convert 8 bytes to a double
var randomDouble = BitConverter.ToDouble(byteArray2, 0);
+4