一个四位数码管循环显示0-9999并且在整数时让蜂鸣器响起来的程序，在keil上编译，下载到51单片机上，连好电路后即可运行。-A four digital tube cyclic display 0-9999 in integer and let a buzzer sounded program, compiled in keil, download to 51 single-chip microcomputer, even after good circuit can operate.