const int trigpin = 7;
const int echopin = 6;
int redled = 11;
int greenled = 12;
long duration;
int distance;

void setup() {
 pinMode(trigpin, OUTPUT);
 pinMode(echopin, INPUT);
 pinMode(redled, OUTPUT);
 pinMode(greenled, OUTPUT);
 Serial.begin(9600);
}


void loop() {



digitalWrite(trigpin, LOW);
delay(2);
digitalWrite(trigpin, HIGH);
delay(10);
digitalWrite(trigpin, LOW);

duration = pulseIn(echopin,HIGH);
//change the duration to cm and find half of it as the distance 
 distance = (duration*0.0343)/2;
//we just print the distance on the serial monitor now 
Serial.print("Distance = ");
Serial.println(distance);
delay(100);

digitalWrite(redled, LOW);
digitalWrite(greenled, LOW);

if (distance < 25) {
  digitalWrite(greenled, HIGH);
}
else {
  digitalWrite(redled, HIGH);
}
delay(100);
}