Simple program to convert string to lower case and allow only letters don't work

Question

can you guys tell me why this program don't change my input string into lower case string containing only letters? I mean only letter part does work but letters don't change to lower case. When I write YELLOW, I should see yellow in the window but I still ses YELLOW all upper case as the output.

namespace ConsoleApplication6
{
class czlowiek
{
    private string _imie;
    private string _nazwisko;
    private int _wiek;

    public string imie
    {
        get
        {
            return _imie;
        }
        set
        {
            for (int i = 0; i < value.Length; i++)
            {
                if (Convert.ToInt32(char.ToLower(value[i])) >= 97 &&     Convert.ToInt32(char.ToLower(value[i])) <= 122)
                    _imie += value[i];
            }
        }

    }

    public string nazwisko
    {
        get
        {
            return _nazwisko;
        }
        set
        {
            for (int i = 0; i < value.Length; i++)
            {
                if (Convert.ToInt32(char.ToLower(value[i])) >= 97 && Convert.ToInt32(char.ToLower(value[i])) <= 122)
                    _nazwisko += value[i];
            }

        }

    }
    public int wiek
    {
        get
        {
            if (_wiek < 0 || _wiek > 100)
                return 0;
            else
                return _wiek;
        }
        set
        {
            if (value < 0 || value > 100)
                Console.WriteLine("Wporwadzona wartość niepoprawna");
            else
                    _wiek = value;
        }
    }

}
}

and main program:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication6
{
class Program
{
    static void Main(string[] args)
    {
        czlowiek admin = new czlowiek();

        Console.Write("Podaj swoje imie: ");
        admin.imie = Console.ReadLine();
        Console.WriteLine("Cześć {0}!", admin.imie);

        Console.WriteLine("Podaj swój wiek: ");
        admin.wiek = int.Parse(Console.ReadLine());
        if (admin.wiek != 0)
             Console.Write("Masz {0}", admin.wiek);


        Console.ReadLine();

    }
}
}

Answer 1

You should set values like this:

_imie += char.ToLower(value[i]);
_nazwisko += char.ToLower(value[i]);