caesers.cs

 public string Encrypt(string word)
        {
            word.ToLower();
            string encryptedWord = "";
            char[] split = word.ToCharArray();
            foreach (char character in split)
            {
                switch (character)
                {
                    case 'a': encryptedWord += "d"; break;
                    case 'b': encryptedWord += "e"; break;
                    case 'c': encryptedWord += "f"; break;
                    case 'd': encryptedWord += "g"; break;
                    case 'e': encryptedWord += "h"; break;
                    case 'f': encryptedWord += "i"; break;
                    case 'g': encryptedWord += "j"; break;
                    case 'h': encryptedWord += "k"; break;
                    case 'i': encryptedWord += "l"; break;
                    case 'j': encryptedWord += "m"; break;
                    case 'k': encryptedWord += "n"; break;
                    case 'l': encryptedWord += "o"; break;
                    case 'm': encryptedWord += "p"; break;
                    case 'n': encryptedWord += "q"; break;
                    case 'o': encryptedWord += "r"; break;
                    case 'p': encryptedWord += "s"; break;
                    case 'q': encryptedWord += "t"; break;
                    case 'r': encryptedWord += "u"; break;
                    case 's': encryptedWord += "v"; break;
                    case 't': encryptedWord += "w"; break;
                    case 'u': encryptedWord += "x"; break;
                    case 'v': encryptedWord += "y"; break;
                    case 'w': encryptedWord += "z"; break;
                    case 'x': encryptedWord += "a"; break;
                    case 'y': encryptedWord += "b"; break;
                    case 'z': encryptedWord += "c"; break;
                }
            }
            return encryptedWord;
        }