Rotational Cipher

using System;

​

public static class RotationalCipher

{

public static string Rotate(string text, int shiftKey){

    string letterN = "";

    shiftKey %= 26;

    foreach(char i in text){

        if(char.IsUpper(i)){

               char res = (char) ('A' + (i - 'A' + shiftKey) % 26);

               letterN += res;

            }

        else if (Char.IsLower(i)){

               char res = (char) ('a' + (i - 'a' + shiftKey) % 26);

               letterN += res;

            }

        

        else {

            letterN += i;

        }

    }

    return letterN;

}

}