Question

How to develop an extension method that may return random character(single character) from alphabet (a,b,….z).

public static char RandomLetter(this char randomchar)
{

}

Answer 1

An extension method is the wrong tool here, since a random letter from the alphabet isn’t related to an input letter (or am I missing something here?).

static string alphabet = "QWERTYUIOPASDFGHJKLZXCVBNM";
static Random = new Random();

public static char RandomLetter()
{
    return alphabet[random.Next(alphabet.Length)];
}

Edit (responding to comments):

You could make it into an extension method on the Random type:

public static char NextRandomLetter(this Random random)
{
    return alphabet[random.Next(alphabet.Length)];
}

(I chose not to call it NextLetterOfTheAlphabet since it obviously should be random)

Thread-safety could be added by synchronizing on a private variable of the class that implements these method. However I think the whole locking process is more CPU taxing than pulling off a random number:

public static char SynchronizedRandomLetter()
{
    lock (random) // Although the lock is not random ;)
    {
        return alphabet[random.Next(alphabet.Length)];
    }
}