说明：  实现单表替换密码，用键盘接收明文和密钥，屏幕打印替换表和密文。明文小写则密文大写，明文大写则密文小写输出。
(Achieve a single table substitution cipher, to receive the plaintext and the key with keyboard, screen printing to replace tables and ciphertext. Plaintext ciphertext uppercase lowercase, uppercase plaintext ciphertext lowercase output.)