how to generate unique random number

Question

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(); } } }

Sachin Singh · Answer

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);

Sachin Singh · Answer

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(); }

Rajanikant Hawaldar · Answer

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 { 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 { if (array[i] == value) return true ; } return false ; } } }

Xaska Dadu · Answer

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