说明：  将ASC的码值在0到127之间的字符写到磁盘文件上，然后从文件中读出这些字符，判断读出的字符是否问可打印字符，若是则在屏幕上直接显示，否则将这些字符的十进制ASC码值输出到屏幕上。
(The ASC code value from 0 to 127 characters written to a disk file, and then read from the file these characters to determine whether the character readout asked printable characters, if it is displayed directly on the screen, otherwise these ASC decimal character code value output to the screen.)