Print Unique keys in C#.net

I am trying to make a key generator that generates upper case, lower case and numeric keys. My current code below generates duplicates keys, using random numbers.

How could I update it to generate unique keys?

 public static void printLowerCaseKeys()
    {
        string array = "";
        int k = 0;
        if (sDelimeterOption == "yes")
        {
            while (k < sKeyLength)
            {
                for (int i = 0; i < sDelimeterCharPosition; i++)
                {
                    if (k >= sKeyLength)
                        break;
                    array = array + (char)r.Next(97, 123);
                    k++;
                }
                if (k < sKeyLength)
                {
                    array = array + sDelimeterChar;
                    k++;
                }
            }
        }
开发者_高级运维        else
        {
            while (k < sKeyLength)
            {
                array = array + (char)r.Next(97, 123);
                k++;
            }
        }
        Console.WriteLine(array);
    }

You could use the GUID class!

Every GUID is unique, even among other systems.

System.GUID.NewGuid().ToString()

You can store existing generated keys and check if the new generated key is already generated or not.

Depending on the required key length, instead of using Random (if 'r' points to Random), you could base your random numbers on Guids (for 128-bit keys) or on what provides the RNGCryptoServiceProvider class.

Guids are fine but if you want something more pretty looking (I.E.: Constrained in certain parts of the string) then you need to sort of do what you are doing, except you need to initialize your random object with a different seed. The best way to do this would be to use a portion of DateTime.Now (second, milliseconds or whatever)