sonar code 2

#define DW digitalWrite
#define PM pinMode
#define H HIGH
#define L LOW
#define OP OUTPUT
#define SB Serial.begin
int pins[3] = {A1,A2,A3};
float duration, distance;
void setup() {
   PM(pins[0],OP);
   PM(pins[1],INPUT);
   PM(pins[2], OP);
   SB(9600);
}

void loop() {
    DW(pins[0],L);
    delay(2);
    DW(pins[0],H);
    delayMicroseconds(10);
    DW(pins[0],L);
    duration = pulseIn(pins[1],H);
    distance = (duration * 0.034 * 0.5);
    if(distance<=100){

          DW(pins[2],H);
    }else{
      DW(pins[2],L);
    }
    delay(500);
}