Đếm số lần nút nhấn hiển thị lên LED 7 thanh SEG

/* Dem so lan nut nhan hien thi len LED 7 thanh*/
#include <REGX51.H>
void delay (unsigned int ms) // Ham tao thoi gian tre
{
unsigned int i ;
unsigned char j ; //khai bien 1 byte
for (i=0;i<ms;i++)
{
for (j=0;j<125;j++)
{}
}}
unsigned char n=0;
unsigned char dongcongtac(void)
{
if(P1_0==0) {
delay(100);
while(P1_0==0)
{
;//khoong lam gi
}
n++;
if(n==10)
{ n=0; }
}
return n;
}
void hienthiso(unsigned char x)
{
switch(x)
{
case 0:{P2=0xff;P2=P2&0x40;break;}
case 1:{P2=0xff;P2=P2&0xf9;break;}
case 2:{P2=0xff;P2=P2&0x24;break;}
case 3:{P2=0xff;P2=P2&0x30;break;}
case 4:{P2=0xff;P2=P2&0x19;break;}
case 5:{P2=0xff;P2=P2&0x12;break;}
case 6:{P2=0xff;P2=P2&0x02;break;}
case 7:{P2=0xff;P2=P2&0xf8;break;}
case 8:{P2=0xff;P2=P2&0x80;break;}
case 9:{P2=0xff;P2=P2&0x10;break;}
}
}
void main(void)//Ham chinh
{
unsigned char m;
while(1)
{
m=dongcongtac();
hienthiso(m);
}
}