C 中的 ROT13 加密代码在小写时失败

Question

这是我的ROT13密码代码。它适用于大写字母，但是当我输入 hello 时，它会返回 [X__b谁能在这里帮助我......

void encrypt(char *cipher,int key) 
{
    int i = 0;
    while(cipher[i] != 'n') 
    {
        if(isalpha(cipher[i]))
        {
            if((cipher[i] + key) > 'Z' || (cipher[i] + key) > 'z')
            {
                cipher[i] = cipher[i] + key - 26;
            }
            else if((cipher[i] + key) >= 'a' && (cipher[i] + key) <= 'z')
            {
                cipher[i] = cipher[i] + key;
            }
            else if((cipher[i] + key) >= 'A' && (cipher[i] + key) <= 'Z')
            {
                cipher[i] = cipher[i] + key;
            }
        }
        i++;
    }
}

Answer 1

此条件

f((cipher[i] + key) > 'Z' || (cipher[i] + key) > 'z')

对于所有小写字母都是正确的，第二部分(cipher[i] + key) > 'z'多余的