void main(){

           trisb=0;
           trisa=0xff;
           portb=0;
           while(1){if(porta.f0==0){portb=(portb<<1)+1;delay_ms(500);}
                         }
                   }

void main()
{trisb=0;
 trisa.f0=1;
 portb=0;
while(1)
loop:
if(porta.f0==0)
              {if(portb==0b11111111){portb=0;delay_ms(1000);goto loop;}
               portb=portb*2+1;
               delay_ms(500);
              }
}