为什么第二次扫描就出错了。。。

#include "reg51.h" #define uint unsigned int
#define uchar unsigned char delay(uint t)
{
uint i,j;
for(i=0;i<t;i++)
for(j=0;j<100;j++)
{};
} sbit DS1=P2^0;
sbit DS2=P2^1; uint wei;
float num; uchar code SHOW[]={0x3F,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71};
scan()
{
uchar i;
for(i=0;i<7;i++)
{ P1=0xdf;
DS1=1;
DS1=0;
wei=num*10;
P1=SHOW[wei/100];
DS2=1;
DS2=0;
delay(10);
P1=0x00;DS2=1;DS2=0;
P1=0xbf;
DS1=1;
DS1=0;
wei=num*10;
P1=SHOW[wei/10%10]|0x80;
DS2=1;
DS2=0;
delay(10); P1=0x00;DS2=1;DS2=0;
P1=0x7f;
DS1=1;
DS1=0;
wei=num*10;
P1=SHOW[wei%10];
DS2=1;
DS2=0;
delay(10); P1=0x00;DS2=1;DS2=0; }
num-=0.1;
if(num==0.0)
num=60.0;
} void main()
{
num=60.0;
while(1)
{
scan();
}
}