编写程序，将键盘接收到的四位十六进制数转换为等值的二进制数，再显示在屏幕上。若输入的不是0-F间的数字,则显示出错信息,并要求重新输入-Preparation procedures, the keyboard received four of sixteen hexadecimal conversion into equivalent binary number, and then displayed on the screen. If the input is not 0-F figures, is to display an error message, and asked to input