这个程序的算法设计求大神指点AT89C51单片机的

#include "reg51.h"
unsigned char data cnt_distance;
unsigned int data D_cnt;
sbit led = P3^7;
sbit add = P1^0;
sbit dec = P1^1;
bit flag;
char code led_seg_code[10]={0x3f,0x06,0x05b,0x04f,0x66,0x6d,0x7d,0x07,0x7f,0x6f};
//led_seg_code[0-9]代表0-9
//-------延时-----------------
void delay(unsigned int i)//延时
{ while(--i); }
//-------初始化变量------------------
void init_variant() //初始化一些变量的内容
{
//unsigned char i;
D_cnt=0; //脉冲的个数
cnt_distance=0; //距离的计数
}
//-------数码管动态扫描-------------
void led_show()
{
unsigned char i,k;
//-----显示距离------
k=cnt_distance; //k = 34;
i=k/10; //暂存百位
P0=led_seg_code[i];
P2&=0xfe;
delay(100);
P2 = 0XFF;
i=k%10;
P0=led_seg_code[i];
P2&=0xfd;
delay(100);
P2 = 0XFF;
}
//----------中断计数-----------
/*
void init0() interrupt 0
{
if(D_cnt<=5) D_cnt++; //计数100次，每次10米，表示一公里
else
{
D_cnt=0;
cnt_distance=cnt_distance+1;
if(cnt_distance >= 34)cnt_distance = 0;
}
}
*/
/*
void init0() interrupt 0
{
D_cnt++;
if(D_cnt>=5) //计数100次，每次10米，表示一公里
{
D_cnt=0;
cnt_distance=cnt_distance+1;
if(cnt_distance >= 34)cnt_distance = 0;
}
}
*/
void caled()
{
led = 0;
delay(5000);
led = 1;
delay(5000);
}
void keyscan()
{
if(add == 0)
{
delay(10000);
if(add == 0)
{
while(!add);
cnt_distance++;
}
}
if(dec == 0)
{
delay(10000);
if(dec == 0)
{
while(!dec);
cnt_distance--;
}
}
}
//---------主程序----------------
void main()
{//初始化各变量
init_variant();
//初始化51的寄存器
TMOD=0x20; //用T1计时 8位自动装载定时模式，不用T0
TH1=0x19; //250微秒溢出一次; 250=(256-x)*12/11.0592 -> x= 230.4
TL1=0x19;
EA=1; //开中断
//EX0 = 1; //开外部中断0
ET1=1;
IT0=1;
TR1=0; //定时器T1
P1 = 0xff;
flag = 0;
while(1)
{
keyscan();
if(IE0==1) //每来1个脉冲，中断一次
{
IE0=0;
D_cnt++;
if(D_cnt>=10) //计数100次，每次10米，表示一公里
{
D_cnt=0;
caled();
caled();
caled();
caled();
if(cnt_distance >= 34)flag = 1;
if(flag==0)cnt_distance=cnt_distance+1;
if(flag == 1)
{
-- cnt_distance;
if(cnt_distance<=0)flag = 0;
}
}
}
led_show();
}
}
//-----公交车自动报站程序结束------------