#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<time.h>
int show(void)
{
char str[100];
time_t t;
struct tm *lt;
t=time(NULL);
lt=localtime(&t);
printf("%s\n",str);
strftime(str,100,"%y-%m-%d %H:%M:%S",lt);
return 0;
}
void sleep(clock_t wait )//设置定时器
{
clock_t goal;
goal=wait+clock();
while(goal>clock());
}
void main()
{
printf("当前日期及时间是\n");
while(true)
{
system("cls");//清屏函数时
show();
sleep(1000);
}
}

不懂，帮顶！

#include<stdio.h>
 #include<stdlib.h>
 #include<string.h>
 #include<time.h>
 int show(void)
 {
     char str[100] ={0};
     time_t t;
     struct tm *lt;
     t=time(NULL);
     lt=localtime(&t);
     strftime(str,100,"%y-%m-%d %H:%M:%S",lt);
     printf("%s\n",str);
     return 0;
 }
 void sleep(clock_t wait )//设置定时器
 {
     clock_t goal;
     goal=wait+clock();
     while(goal>clock());
 }
 void main()
 {
     printf("当前日期及时间是\n");
     while(1)
     {
         system("cls");//清屏函数时
         show();
         sleep(1);
     }
 }
我试过了，一秒钟涮洗一次

你刚刚延迟1000秒，而且数组初始化没清零