How to make random string of numbers and letters with a length of 5? [duplicate]

Answer 1

Use an input array to draw your values from:

private static string RandomString(int length)
{
    const string pool = "abcdefghijklmnopqrstuvwxyz0123456789";
    var builder = new StringBuilder();

    for (var i = 0; i < length; i++)
    {
        var c = pool[random.Next(0, pool.Length)];
        builder.Append(c);
    }

    return builder.ToString();
}

Or the (inevitable) Linq solution:

private static string RandomString(int length)
{
    const string pool = "abcdefghijklmnopqrstuvwxyz0123456789";
    var chars = Enumerable.Range(0, length)
        .Select(x => pool[random.Next(0, pool.Length)]);
    return new string(chars.ToArray());
}

Answer 2

Copying from jon skeet's answer... https://stackoverflow.com/a/976674/67824

Random rand = new Random();

public const string Alphabet = 
"abcdefghijklmnopqrstuvwyxzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

public string GenerateString(int size)
{
    char[] chars = new char[size];
    for (int i=0; i < size; i++)
    {
        chars[i] = Alphabet[rand.Next(Alphabet.Length)];
    }
    return new string(chars);
}

Answer 3

replace

ch = Convert.ToChar(Convert.ToInt32(Math.Floor(26 * random.NextDouble() + 65)));

by

string chars="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
ch=chars[random.Next(chars.Length)];

---

Note that your code doesn't create unpredictable random strings. In particular there are only 2 billion possible results, and if your computer gets restarted often, some of them are much more likely than others.

If you want unpredictable random strings, you should use RNGCryptoServiceProvider. You can fine an example at https://stackoverflow.com/a/1344255/445517 , you just need to add the hyphens.