static bool Integer(int key)
        {
            return (key >= 1 && key <= 255);
        }
        static char EncryptChar(char ch, int key) 
        {
            char newCh = ch;     
                int ascii = (int)ch;//find the ascii code of ch
                int newAscii = ascii ^ key;  
                newCh = Convert.ToChar(newAscii);           
            return newCh;
        }
        static string Encrypt(string word, int key)  
        {
            string newWord = "";
            foreach (char ch in word)
            {
                char newCh = EncryptChar(ch, key);
                newWord=newWord + newCh;
            }
            return newWord;
        }
        static void Main(string[] args)
        {
            Console.Write("Enter a phrase: ");
            string phrase = Console.ReadLine();

            Console.Write("Enter a key: ");
            int key = Convert.ToInt32(Console.ReadLine());
            while (!Integer(key))
            { 
                Console.Write("Enter a character between 1-255: ");
                key = Convert.ToInt32(Console.ReadLine());
            }
            string newPhrase = Encrypt(phrase, key);
            Console.WriteLine("The new phrase is: " + newPhrase);
            Console.ReadLine();
        }