How I do a method to assign random number not repeated to a list of users?

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I need to create an application with mvc arquitecture. I need to generate ramdom numbers 4 digits (not repeated) for users of my app. I mean, this method put on controller user , generate the numbers and show it in a view like a list (user + numbers asign). like a password

Do you have any idea? sorry fr my english
I need it for a test

What I have tried:

 public class User
    {

        [Key]
        public int UserId { get; set; }

       
        public int code { get; set; } // random number

       
        public string Name { get; set; }


        
        

        
    }
}

public class UserController : Controller
   {
       private DbContext db = new DbContext();

       // GET: Users
       public ActionResult Index()
       {
           var users = db.Users.Include(c => c.Lista);
           return View(users.ToList());
       }

Posted 15-Oct-17 13:16pm

NerakSeven

Updated 15-Oct-17 20:54pm

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Patrice T · Answer 1 · 2017-10-15T14:12:00

Quote:
I need to generate ramdom numbers 4 digits (not repeated)

You have to make a choice!
Random and not repeated are mutually exclusive.
Random imply the possibility of repeat, and no repeat imply not random.
If you choose no repeat, think about the Shuffling algorithms
Shuffling - Wikipedia[^]
Other methods that keep track of previously picked number downgrade with quantity of picked numbers as it become more and more difficult to pick an unused number.

phil.o · Answer 2 · 2017-10-15T14:20:00

The code which generates a random number between 1000 and 9999 is

C#

int randomNumber = Random.Next(1000, 10000);

Now, if you want to ensure uniqueness of this number, you have to keep track of previous generated values. Simplest way is to use a HashSet:

C#

HashSet<int> generatedNumbers = new HashSet<int>();
int randomNumber;

// Keep generating a random number until an unused value is found
do {
   randomNumber = Random.Next(1000, 10000);
} while (generatedNumbers.Contains(randomNumber));

generatedNumbers.Add(randomNumber);

// From here you have your random number that you can use
// This number has been added to the set so that it will not be chosen for next usages

Hope this helps. Kindly.

George Swan · Answer 3 · 2017-10-15T20:54:00

I don't know the range of your random numbers, but if it is just a few thousand you could initialise a List and randomly index into the List removing each number chosen as you go. Something like this.

C#

Random random = new Random();
int upperBound = 1000;
List<int> Choices = Enumerable.Range(0, upperBound).ToList();
//Generate 1000 unique random numbers in the inclusive range 0-999
for(int i=0;i<upperBound;i++)
{
int index = random.Next(0, Choices.Count);
int choice = Choices[index];
Choices.RemoveAt(index);
}

How I do a method to assign random number not repeated to a list of users?

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