帮忙看看哪里错了？
#include <reg51.h>
#define uint unsigned int
#define uchar unsigned char
uchar num;
sbit K=P0^0;
void main()
{
K=0 ;
TMOD=0x01;
TH0=0X00;
TL0=0X3D;
EA=1;
TR0=1;
while(1)
{if(TF0==1)
{
TF0=0;
num=num++;
TH0=0X5D;
TL0=0X3D;
}
if(num==20)
{
num=0;
K=~K;}
}
}