Random rastgele = new Random();
string harfler = "ABCÇDEFGĞHIİJKLMNOÖPRSŞTUÜVYZabcçdefgğhıijklmnoöprsştuüvyz";
string uret = "";
for (int i = 0; i < 6; i++)
{
uret += harfler[rastgele.Next(harfler.Length)];
}
Console.WriteLine(uret);
Console.ReadKey();