Is using a GUID a valid way to generate a random string of characters and numbers? [duplicate]

Answer 1

As already stated GUIDs are designed to be unique and not to be random. A better and rather simple way to generate a "random" string (i.e. meeting certain statistical requirements for randomness) would be to use Random:

/// 

/// Generates a random string with the given length
/// 
/// Size of the string
/// If true, generate lowercase string
/// Random string
private string RandomString(int size, bool lowerCase)
{
    StringBuilder builder = new StringBuilder();
    Random random = new Random();
    char ch;
    for (int i = 0; i < size; i++)
    {
        ch = Convert.ToChar(Convert.ToInt32(Math.Floor(26 * random.NextDouble() + 65)));
        builder.Append(ch);
    }
    if (lowerCase)
        return builder.ToString().ToLower();
    return builder.ToString();
}

If you need "more secure" random numbers you might want to check out RNGCryptoServiceProvider. But as already John von Neumann said:

Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin.