// C# Extension Method

// Doc: https://csharp-extension.com/en/method/1002146/string-isletter

​

// @nuget: Z.ExtensionMethods

​

using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        string input = ".NET 4.7.2";

​

        Console.WriteLine("Is each of the following characters a letter?");

​

        for (int i = 0; i < input.Length; i++)

        {

            // C# Extension Method: String - IsLetter

            var result = input.IsLetter(i);

            Console.WriteLine("input[{0}] = {1} ", i, result);

        }

    }

}