cipher caesar

// https://www.hackerrank.com/challenges/caesar-cipher-1/problem?isFullScreen=true

string caesarCipher(string s, int k) {
    string res="";

    for ( auto x : s) {
        if ( isalpha(x) )
        {
            if ( islower(x)){
                if (int(x)+k>int('z')){
                int delta = int(x)+k -int('a');
                delta%=26;
                res+= char(delta+97);
                }else res += char (int(x)+k);
            }
            else {
                if (int(x)+k>int('Z')){
                int delta = int(x)+k -int('A');
                delta%=26;
                res+= char(delta+int('A'));
                }else res += char (int(x)+k);
            }
        }else res+=x;
    }
    return res;
}