说明：  ．文件加密程序 要求：A、文件名从键盘输入。 B、加密密钥从键盘输入。 思路：从原文件读取内容至缓冲区，对其加密后，重新写回文件原来的地方。 提示要点：A、加密可使用“异或”操作。 B、相关中断为3DH，3EH，3FH，40H，42H号系统功能调用（INT 21H）。
(. File encryption program requirements: A, file names from the keyboard. B, the encryption key from the keyboard. Idea: read the content from the original file into the buffer, encrypt, re-write the file back to its original place. Tip points: A, encryption can use the " exclusive or" operation. B, related interrupting 3DH, 3EH, 3FH, 40H, 42H number system function call (INT 21H).)