Question

How to create random X-length string that contains letters and numbers. My fast solution is:

Guid.NewGuid().ToString("N").Substring(X);

Any another better ideas?

Answer 1

If you want “random” strings for dictionary keys, simply use a Guid. They will be unique and more than adequate for keying dictionaries.

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Something like would work, but you need to constrain your random range to avoid shenanigans:

_{Warning, coded it and ran it once – otherwise untested. Performance versus your current solution is unquantified. Also, this implementation is a lot wordier than the answer linked in the question comments.}

    static void Main(string[] args)
    {
        Random r = new Random();

        int x = r.Next(1, 1000);

        char[] pool = new[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z' };
        char[] word = new char[x];

        for (int i = 0; i < x; i++)
        {
            // max value is not inclusive, so no -1 from length.
            int a = r.Next(pool.Length); 
            word[i] = pool[a];
        }

        Console.WriteLine(new string(word));
        Console.ReadLine();
    }

There’s probably a nicer way to do this using the ASCII codes, but meh.