Creating the start of a Caesar cipher
Instead of create the whole list and modify it subsequently, you could calculate the value directly. 


The code could like that:

static void Main()
{
    GettingInput gi = new GettingInput();
    var input = gi.GetInput();
    Console.WriteLine("Your input:\n{0}", input);

    var first = (int)'a';
    var last = (int)'z';
    var length = last - first;

    var query = Enumerable
        .Range(0, length)
        .Select(i =&gt; (char)(first + ((input + i) % length)));

    foreach (var number in query)
        Console.WriteLine(number);

    Console.ReadLine();
}



You could use int.TryParse(Console.ReadLine(), out input) instead of catching the exception