7.2 用全局变量编程模拟显示一个数字时钟

#include <stdio.h>#include <stdlib.h> int hour; int minute; int second; void Update(){    second++;    if(second==60)    {        second=0;        minute++;    }    if(minute==60)    {       minute=0;       hour++;    }    if(hour==24)    {        hour=0;    }}void Display(){    printf("%2d:%2d:%2d\n",hour,minute,second);}void Delay(){    int t;    for(t=0;t<100000000;t++);}int main(){    int i;    hour=minute=second=0;    for(i=0;i<100000000;i++)    {        Update();        Display();        Delay();    }    return 0;}

总结：利用循环结构控制时钟的运行时间。注意要对hour minute second 进行赋初始值0.