文件加密：对给定的ASCII码值进行加密：若字符是英文字母或数字，则用该字符在ASCII码表中位置之后第五位字符进行加密，否则用ASCII码表中位置之前第三位字符进行加密。-File encryption: For a given value of the ASCII code for encryption: If the character is a letter or number, then use the ASCII character code table position after the fifth character is encrypted, or before using ASCII code table position- the third character is encrypted.