using System;

​

public class Program

{

    public static void Main()

    {

        string word = "hello";

        string letter = "o";

        if (Contains(word, letter))

            Console.WriteLine("The word contains the letter");

        else

            Console.WriteLine("The word does not contain the letter");

                string word2 = "hello";

        string letter2 = "x";

        if (Contains(word2, letter2))

            Console.WriteLine("The word contains the letter");

        else

            Console.WriteLine("The word does not contain the letter");

    } 

​

    public static bool Contains(string word, string letter)

    {

        return word != null && word.Contains(letter,  StringComparison.InvariantCultureIgnoreCase);

    }

}

​