C语言凯撒加密

 public string Caesar(int key, string str) {            char[] c = str.ToCharArray();            string strCaesar = "";        for (int i = 0; i < str.Length; i++) {            string ins = c[i].ToString();            string outs = "";            bool isChar = str.Contains(ins.ToLower());            bool isToUpperChar = isChar && (ins.ToUpper() == ins);            ins = ins.ToLower();            if (isChar) {                int offset = (Ascll(ins) + key - Ascll("a")) % (Ascll("z") - Ascll("a") + 1);                outs = Convert.ToChar(offset + Ascll("a")).ToString();                if (isToUpperChar) {                    outs = outs.ToUpper();                }            } else {                outs = ins;            }            strCaesar += outs;        }            for (int i = 0; i < str.Length; i++) {                c[i] += key;            }                return strCaesar;        }        // 字符转ascll        public int Ascll(string str) {            byte[] array = new byte[1];            array = System.Text.Encoding.ASCII.GetBytes(str);            int asciicode = (short)(array[0]);            return asciicode;        }