How to generate random unique 16 digit number in asp.net without collision

Question

how can i generate 16 digit unique random numbers without any repetition in c# asp.net, as i have read the concept of GUID which generate characters along with numbers but i

Answer 1

You can create a random number using the Random class:

private static Random RNG = new Random();

public string Create16DigitString()
{
  var builder = new StringBuilder();
  while (builder.Length < 16) 
  {
    builder.Append(RNG.Next(10).ToString());
  }
  return builder.ToString();
}

Ensuring that there are no collisions requires you to track all results that you have previously returned, which is in effect a memory leak (NB I do not recommend that you use this - keeping track of all previous results is a bad idea, rely on the entropy of a random string of up to 16 characters, if you want more uniqueness, increase the entropy, but I shall include it to show how it could be done):

private static HashSet<string> Results = new HashSet<string>();

public string CreateUnique16DigitString()
{
  var result = Create16DigitString();
  while (!Results.Add(result))
  {
    result = Create16DigitString();
  }

  return result;
}