C51一个按键控制LED四种模式

#include<reg51.h>
sbit S1=P0^0;

void delay(unsigned int i)
{
unsigned int k;
for(k=0;k<i;k++);
}

void main()
{
unsigned char i=0;
P1=0xff;

   while(1)
   {
      if(S1==0)
     {
      delay(1200);
      if(S1==0)
       {if(++i==5)i=1;}     
     }
     switch(i)
     {
      case 1:P1=0x00;break;
      case 2:P1=0x55;break;
      case 3:P1=0x0f;break;
      case 4:P1=0xf0;break;
      default:break;
     }