求助。。

请高手帮我看下这程序。。。为什么个位，十位，百位++不了？谢谢！！

#include<reg52.h>
#define uint unsigned int
#define uchar unsigned char
uchar temp,aa,qian,bai,shi,ge,slnum;
sbit dula=P2^6;
sbit wela=P2^7;
sbit key=P3^4;
uchar code table[]={
0x3f,0x06,0x5b,0x4f,
0x66,0x6d,0x7d,0x07,
0x7f,0x6f,0x77,0x7c,
0x39,0x5e,0x79,0x71};
void display(uchar qian,uchar bai,uchar shi,uchar ge);
void delay(uint z);
void init();
void main()
{
init();//初始化子程序
//TR0=0;
while(1)
{
if(aa==20)
{
aa=0;
temp++;
if(temp==7200)
{
temp=0;
}
qian=temp/600;
bai=temp%600/60;
shi=temp%60/10;
ge=temp%10;
}
display(qian,bai,shi,ge);
if(key==0)
{
delay(5);
if(key==0)
{
TR0=0;
slnum++;
if(slnum==1)
{
ge++;
if(ge==60)
ge=0;
}
if(slnum==2)
{
shi++;
if(shi==60)
shi=0;
}
if(slnum==3)
{
bai++;
if(bai==60)
bai=0;
}
if(slnum==4)
{
TR0=1;
}
}

}
}
}
void delay(uint z)
{
uint x,y;
for(x=z;x>0;x--)
for(y=110;y>0;y--);
}
void display(uchar qian,uchar bai,uchar shi,uchar ge)
{
wela=1;
P0=0xfe;
wela=0;
dula=1;
P0=table[qian];
dula=0;
P0=0xff;
delay(3);
wela=1;
P0=0xfd;
wela=0;
dula=1;
P0=table[bai];
dula=0;
P0=0xff;
delay(3);
wela=1;
P0=0xfb;
wela=0;
dula=1;
P0=table[shi];
dula=0;
P0=0xff;
delay(3);

wela=1;
P0=0xf7;
wela=0;
dula=1;
P0=table[ge];
dula=0;
P0=0xff;
delay(3);
}
void init()
{
wela=0;
dula=0;
temp=0;
TMOD=0x01;
TH0=(65536-50000)/256;
TL0=(65536-50000)%256;
EA=1;
ET0=1;
TR0=1;
}
void timer0() interrupt 1
{
TH0=(65536-50000)/256;
TL0=(65536-50000)%256;
aa++;
}