void common_anode(volatile long input);
void setup(){
  while(1)
  {
    common_anode(1234); 
  } 
}

void common_anode(volatile long input)
{
  volatile long i,j;
  volatile char *ddra,*ddrb,*outa,*outb;
  volatile char thousand,hundred,one,ten;
  volatile char display[10]={0XC0,0XF9,0XA4,0XB0,0X99,0X92,0X82,0XF8,0X80,0X90};
  ddra=0x21;outa=0x22;ddrb=0x24;outb=0x25;
  *ddra=0xff;*ddrb=0x0f;
  thousand=input/1000;
  hundred=(input%1000)/100;
  ten=(input%100)/10;
  one=input%10;
    *outb=0x01;
    *outa=display[thousand];
    *outa=0xff;
    for(i=0;i<10000;i++);

    *outb=0x02;
    *outa=display[hundred];
    *outa=0xff;
    for(i=0;i<10000;i++);

    *outb=0x04;
    *outa=display[ten];
    *outa=0xff;
    for(i=0;i<10000;i++);

    *outb=0x08;
    *outa=display[one];
    *outa=0xff;
    for(i=0;i<10000;i++);
  
}